Chemistry: The Central Science in SI Units, Global Edition

Theodore L. Brown, Matthew W. Stoltzfus, Michael W. Lufaso

Chapter 5

Thermochemistry - all with Video Answers

Educators

Chapter Questions

Problem 1

Two positively charged spheres, each with a charge of $2.0 \times$ $10^{-5} \mathrm{C}$, a mass of $1.0 \mathrm{~kg}$, and separated by a distance of $1.0 \mathrm{~cm}$, are held in place on a frictionless track.
(a) What is the electrostatic potential energy of this system?
(b) If the spheres are released, will they move toward or away from each other?
(c) What speed will each sphere attain as the distance between the spheres approaches infinity? [Section 5.1]

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 2

The accompanying photo shows a pipevine swallowtail caterpillar climbing up a twig. (a) As the caterpillar climbs, its potential energy is increasing. What source of energy has been used to effect this change in potential energy? (b) If the caterpillar is the system, can you predict the sign of $q$ as the caterpillar climbs? (c) Does the caterpillar do work in climbing the twig? Explain.
(d) Does the amount of work done in climbing a 30-cm section of the twig depend on the speed of the caterpillar's climb? (e) Does the change in potential energy depend on the caterpillar's speed of climb? [Section 5.1]

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 3

Consider the accompanying energy diagram.
(a) Does this diagram represent an increase or decrease in the internal energy of the system?
(b) What sign is given to $\Delta E$ for this process?
(c) If there is no work associated with the process, is it exothermic or endothermic? [Section 5.2]

Matthew Bamidele

Matthew Bamidele

Numerade Educator

Problem 4

The contents of the closed box in each of the following illustrations represent a system, and the arrows show the changes to the system during some process. The lengths of the arrows represent the relative magnitudes of $q$ and $w$. (a) Which of these processes is endothermic? (b) For which of these processes, if any, is $\Delta E<0 ?(\mathbf{c})$ For which process, if any, does the system experience a net gain in internal energy? [Section 5.2]

James Irizarry

Numerade Educator

Problem 5

Imagine that you are climbing a mountain.
(a) Is the distance you travel to the top a state function?
(b) Is the change in elevation between your base camp and the peak a state function? [Section 5.2$]$

Matthew Bamidele

Matthew Bamidele

Numerade Educator

Problem 6

The diagram shows four states of a system, each with different internal energy, E. (a) Which of the states of the system has the greatest internal energy? (b) In terms of the $\Delta E$ values, write two expressions for the difference in internal energy between State A and State B. (c) Write an expression for the difference in energy between State $\mathrm{C}$ and State $\mathrm{D}$.
(d) Suppose there is another state of the system, State E, and its energy relative to State $\mathrm{A}$ is $\Delta E=\Delta E_{1}+\Delta E_{4} .$ Where would State $\mathrm{E}$ be on the diagram? [Section 5.2$]$

James Irizarry

Numerade Educator

Problem 7

You may have noticed that when you compress the air in a bicycle pump, the body of the pump gets warmer. (a) Assuming the pump and the air in it comprise the system, what is the sign of $w$ when you compress the air? (b) What is the sign of $q$ for this process? (c) Based on your answers to parts (a) and (b), can you determine the sign of $\Delta E$ for compressing the air in the pump? If not, what would you expect for the sign of $\Delta E$ ? What is your reasoning? [Section 5.2]

Matthew Bamidele

Matthew Bamidele

Numerade Educator

Problem 8

Imagine a container placed in a tub of water, as depicted in the accompanying diagram. (a) If the contents of the container are the system and heat is able to flow through the container walls, what qualitative changes will occur in the temperatures of the system and in its surroundings? From the system's perspective, is the process exothermic or endothermic? (b) If neither the volume nor the pressure of the system changes during the process, how is the change in internal energy related to the change in enthalpy? [Sections 5.2 and 5.3$]$

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 9

In the accompanying cylinder diagram, a chemical process occurs at constant temperature and pressure. (a) Is the sign of $w$ indicated by this change positive or negative? (b) If the process is endothermic, does the internal energy of the system within the cylinder increase or decrease during the change and is $\Delta E$ positive or negative? [Sections 5.2 and 5.3 ]

Matthew Bamidele

Matthew Bamidele

Numerade Educator

Problem 10

The gas-phase reaction shown, between $\mathrm{N}_{2}$ and $\mathrm{O}_{2}$, was run in an apparatus designed to maintain a constant pressure.
(a) Write a balanced chemical equation for the reaction depicted and predict whether $w$ is positive, negative, or zero.
(b) Using data from Appendix C, determine $\Delta H$ for the formation of one mole of the product. [Sections 5.3 and 5.7$]$

James Irizarry

Numerade Educator

Problem 11

Consider the two diagrams that follow.
(a) Based on (i), write an equation showing how $\Delta H_{\mathrm{A}}$ is related to $\Delta H_{\mathrm{B}}$ and $\Delta H_{\mathrm{C}}$.
(b) Based on (ii), write an equation relating $\Delta H_{Z}$ to the other enthalpy changes in the diagram.
(c) The equations you obtained in parts (a) and (b) are based on what law?
(d) Would similar relationships hold for the work involved in each process? [Section 5.6]

Matthew Bamidele

Matthew Bamidele

Numerade Educator

Problem 12

Consider the conversion of compound A into compound B: $\mathrm{A} \longrightarrow \mathrm{B}$. For both compounds $\mathrm{A}$ and $\mathrm{B}, \Delta H_{f}^{\circ}>0 .$
(a) Sketch an enthalpy diagram for the reaction that is analogous to Figure 5.23 .
(b) Suppose the overall reaction is exothermic. What can you conclude? [Section 5.7]

Nicole Smina

Numerade Educator

Problem 13

(a) What is the electrostatic potential energy (in joules) between an electron and a proton that are separated by $230 \mathrm{pm}$ ?
(b) What is the change in potential energy if the distance separating the electron and proton is increased to $1.0 \mathrm{nm}$ ?
(c) Does the potential energy of the two particles increase or decrease when the distance is increased to $1.0 \mathrm{nm}$ ?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 14

(a) What is the electrostatic potential energy (in joules) between two electrons that are separated by $460 \mathrm{pm} ?$
(b) What is the change in potential energy if the distance separating the two electrons is increased to $1.0 \mathrm{nm}$ ?
(c) Does the potential energy of the two particles increase or decrease when the distance is increased to $1.0 \mathrm{nm}$ ?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 15

(a) The electrostatic force (not energy) of attraction between two oppositely charged objects is given by the equation $F=\kappa\left(Q_{1} Q_{2} / d^{2}\right)$ where $\kappa=8.99 \times 10^{9} \mathrm{~N}-\mathrm{m}^{2} / \mathrm{C}^{2}, Q_{1}$ and
$Q_{2}$ are the charges of the two objects in Coulombs, and $d$ is the distance separating the two objects in meters. What is the electrostatic force of attraction (in Newtons) between an electron and a proton that are separated by $0.23 \mathrm{nm} ?$
(b) The force of gravity acting between two objects is given by the equation $F=G\left(m_{1} m_{2} / d^{2}\right)$ where $G$ is the gravitational constant, $G=6.674 \times 10^{-11} \mathrm{~N}-\mathrm{m}^{2} / \mathrm{kg}^{2}, m_{1}$ and $m_{2}$
are the masses of the two objects, and $d$ is the distance separating them. What is the gravitational force of attraction (in Newtons) between the electron and proton?
(c) How many times larger is the electrostatic force of attraction?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 16

Use the equations given in Problem 5.15 to calculate: $(\mathbf{a})$ The electrostatic force of repulsion for two electrons separated by 75 pm. $(\mathbf{b})$ The gravitational force of attraction for two electrons separated by $75 \mathrm{pm} .(\mathbf{c})$ If allowed to move, will the electrons be repelled or attracted to one another?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 17

A sodium ion, $\mathrm{Na}^{+}$, with a charge of $1.6 \times 10^{-19} \mathrm{C}$ and a chloride ion, $\mathrm{Cl}^{-}$, with charge of $-1.6 \times 10^{-19} \mathrm{C}$, are separated by a distance of $0.50 \mathrm{nm}$. How much work would be required to increase the separation of the two ions to an infinite distance?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 18

A magnesium ion, $\mathrm{Mg}^{2+}$, with a charge of $3.2 \times 10^{-19} \mathrm{C}$ and an oxide ion, $\mathrm{O}^{2-},$ with a charge of $-3.2 \times 10^{-19} \mathrm{C},$ are separated by a distance of $0.35 \mathrm{nm}$. How much work would be required to increase the separation of the two ions to an infinite distance?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 19

Identify the force present and explain whether work is being
(a) You lift a book off the top performed in the following cases: of a desk.
(b) Air is compressed in a bicycle pump.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 20

Identify the force present and explain whether work is done when
(a) an electron moves in a circle at a fixed distance from a proton,
$(\mathbf{b})$ an iron nail is attracted by and pulled onto a magnet.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 21

(a) Which of the following cannot leave or enter a closed system: heat, work, or matter?
(b) Which cannot leave or enter an isolated system?
(c) What do we call the part of the universe that is not part of the system?

Matthew Bamidele

Matthew Bamidele

Numerade Educator

Problem 22

In a thermodynamic study, a scientist focuses on the properties of a solution in an apparatus as illustrated. A solution is continuously flowing into the apparatus at the top and out at the bottom, such that the amount of solution in the apparatus is constant with time.
(a) Is the solution in the apparatus a closed system, open system, or isolated system?
(b) If the inlet and outlet were closed, what type of system would it be?

James Irizarry

Numerade Educator

Problem 23

(a) According to the first law of thermodynamics, what quantity is conserved?
(b) What is meant by the internal energy of a system?
(c) By what means can the internal energy of a closed system increase?

Matthew Bamidele

Matthew Bamidele

Numerade Educator

Problem 24

(a) Write an equation that expresses the first law of thermodynamics in terms of heat and work.
(b) Under what conditions will the quantities $q$ and $w$ be negative numbers?

James Irizarry

Numerade Educator

Problem 25

Calculate $\Delta E$ and determine whether the process is endothermic or exothermic for the following cases:
$(\mathbf{a}) q=0.763 \mathrm{~kJ}$ and $w=-840 \mathrm{~J}$.
(b) A system releases $66.1 \mathrm{~kJ}$ of heat to its surroundings while the surroundings do $44.0 \mathrm{~kJ}$ of work on the system.

Matthew Bamidele

Matthew Bamidele

Numerade Educator

Problem 26

For the following processes, calculate the change in internal energy of the system and determine whether the process is endothermic or exothermic:
(a) A balloon is cooled by removing $0.655 \mathrm{~kJ}$ of heat. It shrinks on cooling, and the atmosphere does $382 \mathrm{~J}$ of work on the balloon.
(b) A 100.0-g bar of gold is heated from $25^{\circ} \mathrm{C}$ to $50^{\circ} \mathrm{C}$ during which it absorbs $322 \mathrm{~J}$ of heat. Assume the volume of the gold bar remains constant.

James Irizarry

Numerade Educator

Problem 27

A gas is confined to a cylinder fitted with a piston and an electrical heater, as shown here:
Suppose that current is supplied to the heater so that $100 \mathrm{~J}$ of energy is added. Consider two different situations. In case (1) the piston is allowed to move as the energy is added. In case (2) the piston is fixed so that it cannot move.
(a) In which case does the gas have the higher temperature after addition of the electrical energy?
(b) Identify the sign (positive, negative, or zero) of $q$ and $w$ in each case?
(c) In which case is $\Delta E$ for the system (the gas in the cylinder) larger?

Matthew Bamidele

Matthew Bamidele

Numerade Educator

Problem 28

Consider a system consisting of two oppositely charged spheres hanging by strings and separated by a distance $r_{1}$, as shown in the accompanying illustration. Suppose they are separated to a larger distance $r_{2}$, by moving them apart.
(a) What change, if any, has occurred in the potential energy of the system?
(b) What effect, if any, does this process have on the value of $\Delta E ?
(\mathbf{c})$ What can you say about $q$ and $w$ for this process?

James Irizarry

Numerade Educator

Problem 29

(a) What is meant by the term state function?
(b) Give an example of a quantity that is a state function and one that is not.
(c) Is the volume of a system a state function? Why or why not?

Matthew Bamidele

Matthew Bamidele

Numerade Educator

Problem 30

Indicate which of the following is independent of the path by which a change occurs: (a) the change in potential energy when a book is transferred from table to shelf, (b) the heat evolved when a cube of sugar is oxidized to $\mathrm{CO}_{2}(g)$ and $\mathrm{H}_{2} \mathrm{O}(g),(\mathbf{c})$ the work accomplished in burning a gallon of gasoline.

James Irizarry

Numerade Educator

Problem 31

During a deep breath, our lungs expand about $2.0 \mathrm{~L}$ against an external pressure of $101.3 \mathrm{kPa}$. How much work is involved in this process (in J)?

Nicole Smina

Numerade Educator

Problem 32

How much work (in J) is involved in a chemical reaction if the volume decreases from $33.6 \mathrm{~L}$ to $11.2 \mathrm{~L}$ against a constant pressure of $90.5 \mathrm{kPa}$ ?

Nicole Smina

Numerade Educator

Problem 33

(a) Why is the change in internal energy $\Delta E$ usually harder to measure than the change in enthalpy $\Delta H ?(\mathbf{b}) E$ is a state function, but $q$ is not a state function. Explain. (c) For a given process at constant pressure, $\Delta H$ is negative. Is the process endothermic or exothermic?

Nicole Smina

Numerade Educator

Problem 34

(a) Under what condition will the enthalpy change of a process equal the amount of heat transferred into or out of the system?
(b) During a constant-pressure process, the system releases heat to the surroundings. Does the enthalpy of the system increase or decrease during the process?
(c) In a constant-pressure process, $\Delta H=0$. What can you conclude about $\Delta E, q,$ and $w ?$

James Irizarry

Numerade Educator

Problem 35

Assume that 2 moles of water are formed according to the following reaction at constant pressure $(101.3 \mathrm{kPa})$ and constant temnerature $(298 \mathrm{~K});$
$$
2 \mathrm{H}_{2}(g)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{H}_{2} \mathrm{O}(l)
$$
(a) Calculate the pressure-volume work for this reaction.
(b) Calculate $\Delta E$ for the reaction using your answer to (a).

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 36

Suppose that the gas-phase reaction $2 \mathrm{NO}(g)+\mathrm{O}_{2}(g) \longrightarrow$ $2 \mathrm{NO}_{2}(g)$ were carried out in a constant-volume container at constant temperature.
(a) Would the measured heat change represent $\Delta H$ or $\Delta E$ ?
(b) If there is a difference, which quantity is larger for this reaction?
(c) Explain your answer to part (b).

James Irizarry

Numerade Educator

Problem 37

A gas is confined to a cylinder under constant atmospheric pressure, as illustrated in Figure 5.4 . When the gas undergoes a particular chemical reaction, it absorbs $824 \mathrm{~J}$ of heat from its surroundings and has $0.65 \mathrm{~kJ}$ of $P-V$ work done on it by its surroundings. What are the values of $\Delta H$ and $\Delta E$ for this process?

Matthew Bamidele

Matthew Bamidele

Numerade Educator

Problem 38

A gas is confined to a cylinder under constant atmospheric pressure, as illustrated in Figure 5.4. When $0.49 \mathrm{~kJ}$ of heat is added to the gas, it expands and does $214 \mathrm{~J}$ of work on the surroundings. What are the values of $\Delta H$ and $\Delta E$ for this process?

James Irizarry

Numerade Educator

Problem 39

The complete combustion of methane, $\mathrm{CH}_{4}(g)$, to form $\mathrm{H}_{2} \mathrm{O}(l)$ and $\mathrm{CO}_{2}(g)$ at constant pressure releases $890 \mathrm{~kJ}$ of heat per mole of $\mathrm{CH}_{4}$.
(a) Write a balanced thermochemical equation for this reaction.
(b) Draw an enthalpy diagram for the reaction.

Nicole Smina

Numerade Educator

Problem 40

The decomposition of sodium bicarbonate (baking soda), $\mathrm{NaHCO}_{3}(s)$, into $\mathrm{Na}_{2} \mathrm{CO}_{3}(s), \mathrm{H}_{2} \mathrm{O}(l)$, and $\mathrm{CO}_{2}(g)$ at constant pressure requires the addition of $85 \mathrm{~kJ}$ of heat per two moles of $\mathrm{NaHCO}_{3} .$
(a) Write a balanced thermochemical equation for the reaction.
(b) Draw an enthalpy diagram for the reaction.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 41

Atomic hydrogen (H) is used in welding (AHW). The atoms recombine to hydrogen molecules with a large release of heat according to the following reaction:
$$
2 \mathrm{H}(g) \longrightarrow \mathrm{H}_{2}(g)
$$
(a) Using the thermodynamic data in Appendix C, calculate the enthalpy change for this reaction per mole of $\mathrm{H}_{2}$.
(b) Which has the higher enthalpy under these conditions, $2 \mathrm{H}(g)$ or $\mathrm{H}_{2}(g) ?$

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 42

Without referring to tables, predict which of the following has the higher enthalpy in each case: (a) $1 \mathrm{~mol} \mathrm{I}_{2}(s)$ or $1 \mathrm{~mol} \mathrm{I}_{2}(g)$ at the same temperature,
(b) $2 \mathrm{~mol}$ of iodine atoms or $1 \mathrm{~mol}$ of $\mathrm{I}_{2},(\mathbf{c}) 1 \mathrm{~mol} \mathrm{I}_{2}(g)$ and $1 \mathrm{~mol} \mathrm{H}_{2}(g)$ at
$25^{\circ} \mathrm{C}$ or $2 \mathrm{~mol} \mathrm{HI}(g)$ at $25^{\circ} \mathrm{C},(\mathbf{d}) 1 \mathrm{~mol} \mathrm{H}_{2}(g)$ at $100^{\circ} \mathrm{C}$ or
$1 \mathrm{~mol} \mathrm{H}_{2}(g)$ at $300^{\circ} \mathrm{C}$.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 43

Consider the following reaction:
$$
2 \mathrm{Mg}(s)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{MgO}(s) \quad \Delta H=-1204 \mathrm{~kJ}
$$
(a) Is this reaction exothermic or endothermic?
(b) Calculate the amount of heat transferred when $3.55 \mathrm{~g}$ of $\mathrm{Mg}(s)$ reacts at constant pressure.
(c) How many grams of $\mathrm{MgO}$ are produced during an enthalpy change of $-234 \mathrm{~kJ}$ ?
(d) How many kilojoules of heat are absorbed when $40.3 \mathrm{~g}$ of $\mathrm{MgO}(s)$ is decomposed into $\mathrm{Mg}(s)$ and $\mathrm{O}_{2}(g)$ at constant pressure?

Kratika Bhadauria

Kratika Bhadauria

Numerade Educator

Problem 44

Consider the following reaction:
$$
2 \mathrm{CH}_{3} \mathrm{OH}(g) \longrightarrow 2 \mathrm{CH}_{4}(g)+\mathrm{O}_{2}(g) \quad \Delta H=+252.8 \mathrm{~kJ}
$$
(a) Is this reaction exothermic or endothermic? (b) Calculate the amount of heat transferred when $24.0 \mathrm{~g}$ of $\mathrm{CH}_{3} \mathrm{OH}(g)$ is decomposed by this reaction at constant pressure. (c) For a given sample of $\mathrm{CH}_{3} \mathrm{OH},$ the enthalpy change during the reaction is $82.1 \mathrm{~kJ}$. How many grams of methane gas are produced? (d) How many kilojoules of heat are released when $38.5 \mathrm{~g}$ of $\mathrm{CH}_{4}(g)$ reacts completely with $\mathrm{O}_{2}(g)$ to form $\mathrm{CH}_{3} \mathrm{OH}(g)$ at constant pressure?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 45

When solutions containing silver ions and chloride ions are mixed, silver chloride precipitates
$$
\mathrm{Ag}^{+}(a q)+\mathrm{Cl}^{-}(a q) \longrightarrow \operatorname{AgCl}(s) \quad \Delta H=-65.5 \mathrm{~kJ}
$$
(a) Calculate $\Delta H$ for the production of $0.450 \mathrm{~mol}$ of $\mathrm{AgCl}$ by this reaction.
(b) Calculate $\Delta H$ for the production of $9.00 \mathrm{~g}$ of $\mathrm{AgCl} .
(\mathbf{c})$ Calculate $\Delta H$ when $9.25 \times 10^{-4} \mathrm{~mol}$ of $\mathrm{AgCl}$ dissolves in water.

Matthew Bamidele

Matthew Bamidele

Numerade Educator

Problem 46

At one time, a common means of forming small quantities of oxygen gas in the laboratory was to heat $\mathrm{KClO}_{3}$ :
$$
2 \mathrm{KClO}_{3}(s) \longrightarrow 2 \mathrm{KCl}(s)+3 \mathrm{O}_{2}(g) \quad \Delta H=-89.4 \mathrm{~kJ}
$$
For this reaction, calculate $\Delta H$ for the formation of (a) $1.36 \mathrm{~mol}$ of $\mathrm{O}_{2}$ and $(\mathbf{b}) 10.4 \mathrm{~g}$ of $\mathrm{KCl} .(\mathbf{c})$ The decomposition of $\mathrm{KClO}_{3}$ proceeds spontaneously when it is heated. Do you think that the reverse reaction, the formation of $\mathrm{KClO}_{3}$ from $\mathrm{KCl}$ and $\mathrm{O}_{2},$ is likely to be feasible under ordinary conditions? Explain your answer.

James Irizarry

Numerade Educator

Problem 47

Consider the combustion of liquid methanol, $\mathrm{CH}_{3} \mathrm{OH}(l):$
$$
\begin{aligned}
\mathrm{CH}_{3} \mathrm{OH}(l)+\frac{3}{2} \mathrm{O}_{2}(g) \longrightarrow \mathrm{CO}_{2}(g)+2 \mathrm{H}_{2} \mathrm{O}(l) & \\
\Delta H=&-726.5 \mathrm{~kJ}
\end{aligned}
$$
(a) What is the enthalpy change for the reverse reaction?
(b) Balance the forward reaction with whole-number coefficients. What is $\Delta H$ for the reaction represented by this equation?
(c) Which is more likely to be thermodynamically favored, the forward reaction or the reverse reaction?
(d) If the reaction were written to produce $\mathrm{H}_{2} \mathrm{O}(g)$ instead of $\mathrm{H}_{2} \mathrm{O}(l),$ would you expect the magnitude of $\Delta H$ to increase, decrease, or stay the same? Explain.

Matthew Bamidele

Matthew Bamidele

Numerade Educator

Problem 48

Consider the decomposition of liquid benzene, $\mathrm{C}_{6} \mathrm{H}_{6}(l),$ to gaseous acetylene, $\mathrm{C}_{2} \mathrm{H}_{2}(g)$ :
$$
\mathrm{C}_{6} \mathrm{H}_{6}(l) \longrightarrow 3 \mathrm{C}_{2} \mathrm{H}_{2}(g) \quad \Delta H=+630 \mathrm{~kJ}
$$
(a) What is the enthalpy change for the reverse reaction?
(b) What is $\Delta H$ for the formation of 1 mol of acetylene?
(c) Which is more likely to be thermodynamically favored, the forward reaction or the reverse reaction?
(d) If $\mathrm{C}_{6} \mathrm{H}_{6}(g)$ were consumed instead of $\mathrm{C}_{6} \mathrm{H}_{6}(l),$ would you expect the magnitude of $\Delta H$ to increase, decrease, or stay the same? Explain.

James Irizarry

Numerade Educator

Problem 49

(a) Derive an equation to convert the specific heat of a pure substance to its molar heat capacity.
(b) The specific heat of aluminum is $0.9 \mathrm{~J} /(\mathrm{g} \cdot \mathrm{K}) .$ Calculate its molar heat capacity.
(c) If you know the specific heat of aluminum, what additional information do you need to calculate the heat capacity of a particular piece of an aluminum component?

Nicole Smina

Numerade Educator

Problem 50

Two solid objects, A and B, are placed in boiling water and allowed to come to the temperature of the water. Each is then lifted out and placed in separate beakers containing $1000 \mathrm{~g}$ of water at $10.0^{\circ} \mathrm{C}$. Object A increases the water temperature by $3.50^{\circ} \mathrm{C} ; \mathrm{B}$ increases the water temperature by $2.60{ }^{\circ} \mathrm{C}$.
(a) Which object has the larger heat capacity?
(b) What can you say about the specific heats of $\mathrm{A}$ and $\mathrm{B}$ ?

James Irizarry

Numerade Educator

Problem 51

(a) What amount of heat (in joules) is required to raise the temperature of $1 \mathrm{~g}$ of water by 1 kelvin?
(b) What amount of heat (in joules) is required to raise the temperature of 1 mole of water by 1 kelvin?
(c) What is the heat capacity of $370 \mathrm{~g}$ of liquid water?
(d) How many kJ of heat are needed to raise the temperature of $5.00 \mathrm{~kg}$ of liquid water from 24.6 to $46.2^{\circ} \mathrm{C} ?$

Nicole Smina

Numerade Educator

Problem 52

(a) Which substance in Table 5.2 requires the smallest amount of energy to increase the temperature of $50.0 \mathrm{~g}$ of that substance by $10 \mathrm{~K} ?$
(b) Calculate the energy needed for this temperature change.

James Irizarry

Numerade Educator

Problem 53

The specific heat of octane, $\mathrm{C}_{8} \mathrm{H}_{18}(l),$ is $2.22 \mathrm{~J} / \mathrm{g}$ -K. $(\mathbf{a})$ How many J of heat are needed to raise the temperature of $80.0 \mathrm{~g}$ of octane from 10.0 to $25.0^{\circ} \mathrm{C} ?(\mathbf{b})$ Which will require more heat, increasing the temperature of $1 \mathrm{~mol}$ of $\mathrm{C}_{8} \mathrm{H}_{18}(l)$ by a certain amount or increasing the temperature of $1 \mathrm{~mol}$ of $\mathrm{H}_{2} \mathrm{O}(l)$ by the same amount?

Matthew Bamidele

Matthew Bamidele

Numerade Educator

Problem 54

Consider the data about gold metal in Exercise $5.26(\mathrm{~b})$
(a) Based on the data, calculate the specific heat of $\mathrm{Au}(s)$
(b) Suppose that the same amount of heat is added to two $10.0-g$ blocks of metal, both initially at the same temperature. One block is gold metal, and one is iron metal. Which block will have the greater rise in temperature after the addition of the heat?
(c) What is the molar heat capacity of $\mathrm{Au}(s) ?$

James Irizarry

Numerade Educator

Problem 55

When an 18.6-g sample of solid potassium hydroxide dissolves in $200.0 \mathrm{~g}$ of water in a coffee-cup calorimeter (Figure 5.18), the temperature rises from 23.7 to $44.5^{\circ} \mathrm{C}$.
(a) Calculate the quantity of heat (in kJ) released in the reaction.
(b) Using your result from part (a), calculate $\Delta H$ (in kJ/mol KOH) for the solution process. Assume that the specific heat of the solution is the same as that of pure water.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 56

(a) When an 8.50 -g sample of solid ammonium nitrate (NH $\left._{4} \mathrm{NO}_{3}(s)\right)$ dissolves in $120.0 \mathrm{~g}$ of water in a coffee-cup calorimeter (Figure 5.18), the temperature drops from 24.0 to $18.9^{\circ} \mathrm{C}$. Calculate $\Delta H\left(\right.$ in $\left.\mathrm{kJ} / \mathrm{mol} \mathrm{NH}_{4} \mathrm{NO}_{3}\right)$ for the solution process:
$$
\mathrm{NH}_{4} \mathrm{NO}_{3}(s) \longrightarrow \mathrm{NH}_{4}^{+}(a q)+\mathrm{NO}_{3}^{-}(a q)
$$
Assume that the specific heat of the solution is the same as that of pure water.
(b) Is this process endothermic or exothermic?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 57

A 1.50 -g sample of quinone $\left(\mathrm{C}_{6} \mathrm{H}_{4} \mathrm{O}_{2}\right)$ is burned in a bomb calorimeter whose total heat capacity is $8.500 \mathrm{~kJ} /{ }^{\circ} \mathrm{C}$. The temperature of the calorimeter increases from 25.00 to $29.49^{\circ} \mathrm{C}$.
(a) Write a balanced chemical equation for the bomb calorimeter reaction.
(b) What is the heat of combustion per gram of quinone and per mole of quinone?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 58

A 2.20-g sample of phenol $\left(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{OH}\right)$ was burned in a bomb calorimeter whose total heat capacity is $11.90 \mathrm{~kJ} /{ }^{\circ} \mathrm{C} .$ The temperature of the calorimeter plus contents increased from 21.50 to $27.50^{\circ} \mathrm{C} .(\mathbf{a})$ Write a balanced chemical equation for the bomb calorimeter reaction. (b) What is the heat of combustion per gram of phenol and per mole of phenol?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 59

Under constant-volume conditions, the heat of combustion of sucrose $\left(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}\right)$ is $16.49 \mathrm{~kJ} / \mathrm{g}$. A $3.00-\mathrm{g}$ sample of sucrose is burned in a bomb calorimeter. The temperature of the calorimeter increases from 21.94 to $24.62^{\circ} \mathrm{C} .(\mathbf{a})$ What is the total heat capacity of the calorimeter? (b) If the size of the sucrose sample had been exactly twice as large, what would the temperature change of the calorimeter have been?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 60

Under constant-volume conditions, the heat of combustion of naphthalene $\left(\mathrm{C}_{10} \mathrm{H}_{8}\right)$ is $40.18 \mathrm{~kJ} / \mathrm{g}$. A 2.50 -g sample of naphthalene is burned in a bomb calorimeter. The temperature of the calorimeter increases from 21.50 to $28.83^{\circ} \mathrm{C}$. (a) What is the total heat capacity of the calorimeter? (b) A 1.50-g sample of a new organic substance is combusted in the same calorimeter. The temperature of the calorimeter increases from 21.14 to $25.08^{\circ} \mathrm{C}$. What is the heat of combustion per gram of the new substance? (c) Suppose that in changing samples, a portion of the water in the calorimeter were lost. In what way, if any, would this change the heat capacity of the calorimeter?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 61

Can you use an approach similar to Hess's law to calculate the change in internal energy, $\Delta E,$ for an overall reaction by summing the $\Delta E$ values of individual reactions that add up to give the desired overall reaction?

Matthew Bamidele

Matthew Bamidele

Numerade Educator

Problem 62

Consider the following hypothetical reactions:
$$
\begin{array}{l}
\mathrm{A} \longrightarrow \mathrm{B} \quad \Delta H_{I}=+60 \mathrm{~kJ} \\
\mathrm{~B} \longrightarrow \mathrm{C} \quad \Delta H_{I I}=-90 \mathrm{~kJ}
\end{array}
$$
(a) Use Hess's law to calculate the enthalpy change for the reaction $\mathrm{A} \longrightarrow \mathrm{C}$.
(b) Construct an enthalpy diagram for substances A, B, and C, and show how Hess's law applies.

Nicole Smina

Numerade Educator

Problem 63

Calculate the enthalpy change for the reaction
$$
\mathrm{P}_{4} \mathrm{O}_{6}(s)+2 \mathrm{O}_{2}(g) \longrightarrow \mathrm{P}_{4} \mathrm{O}_{10}(s)
$$
given the following enthalpies of reaction:
$$
\begin{array}{ll}
\mathrm{P}_{4}(s)+3 \mathrm{O}_{2}(g) \longrightarrow \mathrm{P}_{4} \mathrm{O}_{6}(s) & \Delta H=-1640.1 \mathrm{~kJ} \\
\mathrm{P}_{4}(s)+5 \mathrm{O}_{2}(g) \longrightarrow \mathrm{P}_{4} \mathrm{O}_{10}(s) & \Delta H=-2940.1 \mathrm{~kJ}
\end{array}
$$

Matthew Bamidele

Matthew Bamidele

Numerade Educator

Problem 64

From the enthalpies of reaction
$$
\begin{aligned}
2 \mathrm{C}(s)+\mathrm{O}_{2}(g) & \longrightarrow 2 \mathrm{CO}(g) & \Delta H=-221.0 \mathrm{~kJ} \\
2 \mathrm{C}(s)+\mathrm{O}_{2}(g)+4 \mathrm{H}_{2}(g) & \longrightarrow & 2 \mathrm{CH}_{3} \mathrm{OH}(g) & \Delta H=-402.4 \mathrm{~kJ}
\end{aligned}
$$
calculate $\Delta H$ for the reaction
$$
\mathrm{CO}(g)+2 \mathrm{H}_{2}(g) \longrightarrow \mathrm{CH}_{3} \mathrm{OH}(g)
$$

James Irizarry

Numerade Educator

Problem 65

From the enthalpies of reaction
$$
\begin{aligned}
\mathrm{H}_{2}(g)+\mathrm{F}_{2}(g) & \longrightarrow 2 \mathrm{HF}(g) & & \Delta H=-537 \mathrm{~kJ} \\
\mathrm{C}(s)+2 \mathrm{~F}_{2}(g) & \longrightarrow \mathrm{CF}_{4}(g) & & \Delta H=-680 \mathrm{~kJ} \\
2 \mathrm{C}(s)+2 \mathrm{H}_{2}(g) & \longrightarrow \mathrm{C}_{2} \mathrm{H}_{4}(g) & & \Delta H=+52.3 \mathrm{~kJ}
\end{aligned}
$$
calculate $\Delta H$ for the reaction of ethylene with $\mathrm{F}_{2}$ :
$$
\mathrm{C}_{2} \mathrm{H}_{4}(g)+6 \mathrm{~F}_{2}(g) \longrightarrow 2 \mathrm{CF}_{4}(g)+4 \mathrm{HF}(g)
$$

Matthew Bamidele

Matthew Bamidele

Numerade Educator

Problem 66

Given the data
$$
\begin{aligned}
\mathrm{N}_{2}(g)+\mathrm{O}_{2}(g) \longrightarrow & 2 \mathrm{NO}(g) & & \Delta H=+180.7 \mathrm{~kJ} \\
2 \mathrm{NO}(g)+\mathrm{O}_{2}(g) & \longrightarrow 2 \mathrm{NO}_{2}(g) & \Delta H &=-113.1 \mathrm{~kJ} \\
2 \mathrm{~N}_{2} \mathrm{O}(g) \longrightarrow & 2 \mathrm{~N}_{2}(g)+\mathrm{O}_{2}(g) & \Delta H &=-163.2 \mathrm{~kJ}
\end{aligned}
$$
use Hess's law to calculate $\Delta H$ for the reaction
$$
\mathrm{N}_{2} \mathrm{O}(g)+\mathrm{NO}_{2}(g) \longrightarrow 3 \mathrm{NO}(g)
$$

James Irizarry

Numerade Educator

Problem 67

(a) What is meant by the term standard conditions with reference to enthalpy changes?
(b) What is meant by the term enthalpy of formation?
(c) What is meant by the term standard enthalpy of formation?

Matthew Bamidele

Matthew Bamidele

Numerade Educator

Problem 68

(a) Why does the standard enthalpy of formation of both the very reactive fluorine $\left(\mathrm{F}_{2}\right)$ and the almost inert gas nitrogen $\left(\mathrm{N}_{2}\right)$ both read zero? (b) Write the chemical equation for the reaction whose enthalpy change is the standard enthalpy of formation of naphthalene $\left(\mathrm{C}_{10} \mathrm{H}_{8}\right)$.

Nicole Smina

Numerade Educator

Problem 69

For each of the following compounds, write a balanced thermochemical equation depicting the formation of one mole of the compound from its elements in their standard states and then look up $\Delta H^{\circ}{ }_{f}$ for each substance in Appendix $\mathrm{C}$.
(a) $\mathrm{NO}_{2}(g),$
(b) $\mathrm{SO}_{3}(g),$
(c) $\mathrm{NaBr}(s),$
(d) $\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2}(s).$

Matthew Bamidele

Matthew Bamidele

Numerade Educator

Problem 70

Write balanced equations that describe the formation of the following compounds from elements in their standard states, and then look up the standard enthalpy of formation for each substance in Appendix C:
(a) $\mathrm{CH}_{3} \mathrm{OH}(l),$
(b) $\mathrm{CaSO}_{4}(s),$
(d) $\mathrm{P}_{4} \mathrm{O}_{6}(s),$
(c) $\mathrm{NO}(g)$.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 71

The following is known as the thermite reaction:
$$
2 \mathrm{Al}(s)+\mathrm{Fe}_{2} \mathrm{O}_{3}(s) \longrightarrow \mathrm{Al}_{2} \mathrm{O}_{3}(s)+2 \mathrm{Fe}(s)
$$
This highly exothermic reaction is used for welding massive units, such as propellers for large ships. Using standard enthalpies of formation in Appendix $\mathrm{C},$ calculate $\Delta H^{\circ}$ for this reaction.

Matthew Bamidele

Matthew Bamidele

Numerade Educator

Problem 72

Acetylene $\left(\mathrm{C}_{2} \mathrm{H}_{2}(g)\right)$ is used for welding because oxyacetylene is the hottest burning common fuel gas. Using standard enthalpies of formation, calculate the quantity of heat produced when $10 \mathrm{~g}$ of acetylene is completely combusted in air under standard conditions.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 73

Using values from Appendix Calculate the standard enthalpy change for each of the following reactions:
(a) $2 \mathrm{SO}_{2}(g)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{SO}_{3}(g)$
(b) $\mathrm{Mg}(\mathrm{OH})_{2}(s) \longrightarrow \mathrm{MgO}(s)+\mathrm{H}_{2} \mathrm{O}(l)$
(c) $\mathrm{N}_{2} \mathrm{O}_{4}(g)+4 \mathrm{H}_{2}(g) \longrightarrow \mathrm{N}_{2}(g)+4 \mathrm{H}_{2} \mathrm{O}(g)$
(d) $\mathrm{SiCl}_{4}(l)+2 \mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{SiO}_{2}(s)+4 \mathrm{HCl}(g)$

Matthew Bamidele

Matthew Bamidele

Numerade Educator

Problem 74

Using values from Appendix C, calculate the value of $\Delta H$ for each of the following reactions:
(a) $\mathrm{CaO}(s)+2 \mathrm{HF}(g) \longrightarrow \mathrm{CaF}_{2}(s)+\mathrm{H}_{2} \mathrm{O}(g)$
(b) $\mathrm{Fe}_{2} \mathrm{O}_{3}(s)+3 \mathrm{C}(s) \longrightarrow 2 \mathrm{Fe}(s)+3 \mathrm{CO}(g)$
(c) $2 \mathrm{CO}(g)+2 \mathrm{NO}(g) \longrightarrow \mathrm{N}_{2}(s)+2 \mathrm{CO}_{2}(g)$
(d) $4 \mathrm{NH}_{3}(g)+5 \mathrm{O}_{2}(g) \longrightarrow 4 \mathrm{NO}(g)+6 \mathrm{H}_{2} \mathrm{O}(g)$

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 75

Complete combustion of 1 mol of acetone $\left(\mathrm{C}_{3} \mathrm{H}_{6} \mathrm{O}\right)$ liberates $1790 \mathrm{~kJ}:$
$$
\begin{aligned}
\mathrm{C}_{3} \mathrm{H}_{6} \mathrm{O}(l)+4 \mathrm{O}_{2}(g) \longrightarrow 3 \mathrm{CO}_{2}(g)+3 \mathrm{H}_{2} \mathrm{O}(l) & \\
\Delta H^{\circ}=&-1790 \mathrm{~kJ}
\end{aligned}
$$
Using this information together with the standard enthalpies of formation of $\mathrm{O}_{2}(g), \mathrm{CO}_{2}(g),$ and $\mathrm{H}_{2} \mathrm{O}(l)$ from Appendix C, calculate the standard enthalpy of formation of acetone.

Matthew Bamidele

Matthew Bamidele

Numerade Educator

Problem 76

Calcium carbide $\left(\mathrm{CaC}_{2}\right)$ reacts with water to form acetylene $\left(\mathrm{C}_{2} \mathrm{H}_{2}\right)$ and $\mathrm{Ca}(\mathrm{OH})_{2}$. From the following enthalpy of reaction data and data in Appendix C, calculate $\Delta H_{f}^{\circ}$ for $\mathrm{CaC}_{2}(s);$
$$
\begin{aligned}
\mathrm{CaC}_{2}(s)+2 \mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{Ca}(\mathrm{OH})_{2}(s)+\mathrm{C}_{2} \mathrm{H}_{2}(g) & \\
\Delta H^{\circ}=&-127.2 \mathrm{~kJ}
\end{aligned}
$$

James Irizarry

Numerade Educator

Problem 77

Gasoline is composed primarily of hydrocarbons, including many with eight carbon atoms, called octanes. One of the cleanest-burning octanes is a compound called 2,3,4 trimethylpentane, which has the following structural formula:
The complete combustion of one mole of this compound to $\mathrm{CO}_{2}(g)$ and $\mathrm{H}_{2} \mathrm{O}(g)$ leads to $\Delta H^{\circ}=-5064.9 \mathrm{~kJ} .$
(a) Write a balanced equation for the combustion of $1 \mathrm{~mol}$ of $\mathrm{C}_{8} \mathrm{H}_{18}(l) .$
(b) By using the information in this problem and data in Table $5.3,$ calculate $\Delta H_{f}^{\circ}$ for 2,3,4 -trimethylpentane.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 78

Diethyl ether, $\mathrm{C}_{4} \mathrm{H}_{10} \mathrm{O}(l)$, a flammable compound that was once used as a surgical anesthetic, has the structure
The complete combustion of $1 \mathrm{~mol}$ of $\mathrm{C}_{4} \mathrm{H}_{10} \mathrm{O}(l)$ to $\mathrm{CO}_{2}(g)$
and $\mathrm{H}_{2} \mathrm{O}(l)$ yields $\Delta H^{\circ}=-2723.7 \mathrm{~kJ} .(\mathbf{a})$ Write a balanced
equation for the combustion of $1 \mathrm{~mol}$ of $\mathrm{C}_{4} \mathrm{H}_{10} \mathrm{O}(l) .(\mathbf{b}) \mathrm{By}$ using the information in this problem and data in Table 5.3 , calculate $\Delta H_{f}^{\circ}$ for diethyl ether.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 79

Ethanol $\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\right)$ is blended with gasoline as an automobile fuel.
(a) Write a balanced equation for the combustion of liquid ethanol in air.
(b) Calculate the standard enthalpy change for the reaction, assuming $\mathrm{H}_{2} \mathrm{O}(g)$ as a product.
(c) Calculate the heat produced per liter of ethanol by combustion of ethanol under constant pressure. Ethanol has a density of $0.789 \mathrm{~g} / \mathrm{mL}$.
(d) Calculate the mass of $\mathrm{CO}_{2}$ produced per kJ of heat emitted.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 80

Methanol $\left(\mathrm{CH}_{3} \mathrm{OH}\right)$ is used as a fuel in race cars.
(a) Write a balanced equation for the combustion of liquid methanol in air.
(b) Calculate the standard enthalpy change for the reaction, assuming $\mathrm{H}_{2} \mathrm{O}(g)$ as a product.
(c) Calculate the heat produced by combustion per liter of methanol. Methanol has a density of $0.791 \mathrm{~g} / \mathrm{mL}$.
(d) Calculate the mass of $\mathrm{CO}_{2}$ produced per kJ of heat emitted.

James Irizarry

Numerade Educator

Problem 81

Without doing any calculations, predict the sign of $\Delta H$ for each of the following reactions:
(a) $\mathrm{NaCl}(s) \longrightarrow \mathrm{Na}^{+}(g)+\mathrm{Cl}^{-}(\mathrm{g})$
(b) $2 \mathrm{H}(g) \longrightarrow \mathrm{H}_{2}(g)$
(c) $\mathrm{Na}(g) \longrightarrow \mathrm{Na}^{+}(g)+\mathrm{e}^{-}$
(d) $\mathrm{I}_{2}(s) \longrightarrow \mathrm{I}_{2}(l)$

Matthew Bamidele

Matthew Bamidele

Numerade Educator

Problem 82

Without doing any calculations, predict the sign of $\Delta H$ for each of the following reactions:
(a) $2 \mathrm{NO}_{2}(g) \longrightarrow \mathrm{N}_{2} \mathrm{O}_{4}(g)$
(b) $2 \mathrm{~F}(g) \longrightarrow \mathrm{F}_{2}(g)$
(c) $\mathrm{Mg}^{2+}(g)+2 \mathrm{Cl}^{-}(g) \longrightarrow \mathrm{MgCl}_{2}(s)$
(d) $\mathrm{HBr}(g) \longrightarrow \mathrm{H}(g)+\mathrm{Br}(g)$

James Irizarry

Numerade Educator

Problem 83

Use bond enthalpies in Table 5.4 to estimate $\Delta H$ for each of the following reactions:
(a) $\mathrm{H}-\mathrm{H}(g)+\mathrm{Br}-\mathrm{Br}(g) \longrightarrow 2 \mathrm{H}-\mathrm{Br}(g)$
(b)

Matthew Bamidele

Matthew Bamidele

Numerade Educator

Problem 84

Use bond enthalpies in Table 5.4 to estimate $\Delta H$ for each of the following reactions:
(a)
(b)

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 85

(a) Use enthalpies of formation given in Appendix C to calculate $\Delta H$ for the reaction $\mathrm{Br}_{2}(g) \longrightarrow 2 \operatorname{Br}(g)$, and use this value to estimate the bond enthalpy $D(\mathrm{Br}-\mathrm{Br})$.
(b) How large is the difference between the value calculated in part (a) and the value given in Table 5.4 ?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 86

(a) The nitrogen atoms in an $\mathrm{N}_{2}$ molecule are held together by a triple bond; use enthalpies of formation in Appendix $\mathrm{C}$ to estimate the enthalpy of this bond, $D(\mathrm{~N} \equiv \mathrm{N}) .(\mathbf{b})$ Consider the reaction between hydrazine and hydrogen to produce ammonia, $\mathrm{N}_{2} \mathrm{H}_{4}(g)+\mathrm{H}_{2}(g) \longrightarrow 2 \mathrm{NH}_{3}(g)$. Use enthalpies of formation and bond enthalpies to estimate the enthalpy of the nitrogen-nitrogen bond in $\mathrm{N}_{2} \mathrm{H}_{4} .(\mathbf{c})$ Based on your answers to parts (a) and (b), would you predict that the nitrogen-nitrogen bond in hydrazine is weaker than, similar to, or stronger than the bond in $\mathrm{N}_{2}$ ?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 87

Consider the reaction $2 \mathrm{H}_{2}(g)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{H}_{2} \mathrm{O}(l)$
(a) Use the bond enthalpies in Table 5.4 to estimate $\Delta H$ for this reaction, ignoring the fact that water is in the liquid state.
(b) Without doing a calculation, predict whether your estimate in part (a) is more negative or less negative than the true reaction enthalpy.
(c) Use the enthalpies of formation in Appendix $\mathrm{C}$ to determine the true reaction enthalpy.

Matthew Bamidele

Matthew Bamidele

Numerade Educator

Problem 88

Consider the reaction $\mathrm{H}_{2}(g)+\mathrm{Br}_{2}(l) \longrightarrow 2 \mathrm{HBr}(g) .(\mathbf{a})$ Use the bond enthalpies in Table 5.4 to estimate $\Delta H$ for this reaction, ignoring the fact that bromine is in the liquid state. (b) Without doing a calculation, predict whether your estimate in part (a) is more negative or less negative than the true reaction enthalpy. (c) Use the enthalpies of formation in Appendix C to determine the true reaction enthalpy.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 89

(a) What is meant by the term fuel value?
(b) Which is a greater source of energy as food, $5 \mathrm{~g}$ of fat or $9 \mathrm{~g}$ of carbohydrate?
(c) The metabolism of glucose produces $\mathrm{CO}_{2}(g)$ and $\mathrm{H}_{2} \mathrm{O}(l)$. How does the human body expel these reaction products?

Matthew Bamidele

Matthew Bamidele

Numerade Educator

Problem 90

(a) Which releases the most energy when metabolized, $1 \mathrm{~g}$ of carbohydrates or $1 \mathrm{~g}$ of fat?
(b) A particular chip snack food is composed of $12 \%$ protein, $14 \%$ fat, and the rest carbohydrate. What percentage of the calorie content of this food is fat?
(c) How many grams of protein provide the same fuel value as $25 \mathrm{~g}$ of fat?

James Irizarry

Numerade Educator

Problem 91

(a) A serving of a particular ready-to-serve brown \& wild rice meal contains $4.5 \mathrm{~g}$ fat, $42 \mathrm{~g}$ carbohydrate, and $4.0 \mathrm{~g}$ protein. Estimate the number of calories in a serving.
(b) According to its nutrition label, the same meal also contains $140 \mathrm{mg}$ of potassium ions. Do you think the potassium contributes to the caloric content of the food?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 92

A hamburger contains $28 \mathrm{~g}$ fat, $46 \mathrm{~g}$ carbohydrate, and $25 \mathrm{~g}$ protein. What is the fuel value in kJ in one hamburger? How many calories does it provide?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 93

The heat of combustion of fructose, $\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6},$ is -2812 $\mathrm{kJ} / \mathrm{mol}$. If a fresh golden delicious apple weighing $120 \mathrm{~g}$ contains $16.0 \mathrm{~g}$ of fructose, what caloric content does the fructose contribute to the apple?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 94

The heat of combustion of ethanol, $\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}(l),$ is -1367 $\mathrm{kJ} / \mathrm{mol}$. A bottle of stout (dark beer) contains up to $6.0 \%$ ethanol by mass. Assuming the density of the beer to be $1.0 \mathrm{~g} / \mathrm{mL},$ what is the caloric content due to the alcohol (ethanol) in a bottle of beer $(500 \mathrm{~mL})$ ?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 95

The standard enthalpies of formation of gaseous propyne $\left(\mathrm{C}_{3} \mathrm{H}_{4}\right),$ propylene $\left(\mathrm{C}_{3} \mathrm{H}_{6}\right),$ and propane $\left(\mathrm{C}_{3} \mathrm{H}_{8}\right)$ are $+185.4,+20.4,$ and $-103.8 \mathrm{~kJ} / \mathrm{mol}$, respectively. (a) Calculate the heat evolved per mole on combustion of each substance to yield $\mathrm{CO}_{2}(g)$ and $\mathrm{H}_{2} \mathrm{O}(g) .$ (b) Calculate the heat evolved on combustion of $1 \mathrm{~kg}$ of each substance. $(\mathbf{c})$ Which is the most efficient fuel in terms of heat evolved per unit mass?

Matthew Bamidele

Matthew Bamidele

Numerade Educator

Problem 96

It is interesting to compare the "fuel value" of a hydrocarbon in a hypothetical world where oxygen is not the combustion agent. The enthalpy of formation of $\mathrm{CF}_{4}(g)$ is $-679.9 \mathrm{~kJ} / \mathrm{mol}$. Which of the following two reactions is the more exothermic?
$$
\begin{aligned}
\mathrm{CH}_{4}(g)+2 \mathrm{O}_{2}(g) & \longrightarrow \mathrm{CO}_{2}(g)+2 \mathrm{H}_{2} \mathrm{O}(g) \\
\mathrm{CH}_{4}(g)+4 \mathrm{~F}_{2}(g) & \longrightarrow \mathrm{CF}_{4}(g)+4 \mathrm{HF}(g)
\end{aligned}
$$

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 97

At the end of 2012, global population was about 7.0 billion people. What mass of glucose in kg would be needed to provide 1500 Cal/person/day of nourishment to the global population for one year? Assume that glucose is metabolized entirely to $\mathrm{CO}_{2}(g)$ and $\mathrm{H}_{2} \mathrm{O}(l)$ according to the following thermochemical equation:
$$
\begin{aligned}
\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}(s)+6 \mathrm{O}_{2}(g) \longrightarrow 6 \mathrm{CO}_{2}(g)+6 \mathrm{H}_{2} \mathrm{O}(l) \\
\Delta H^{\circ} &=-2803 \mathrm{~kJ}
\end{aligned}
$$

Matthew Bamidele

Matthew Bamidele

Numerade Educator

Problem 98

The automobile fuel called E85 consists of $85 \%$ ethanol and 15\% gasoline. E85 can be used in the so-called flex-fuel vehicles (FFVs), which can use gasoline, ethanol, or a mix as fuels. Assume that gasoline consists of a mixture of octanes (different isomers of $\mathrm{C}_{8} \mathrm{H}_{18}$ ), that the average heat of combustion of $\mathrm{C}_{8} \mathrm{H}_{18}(l)$ is $5400 \mathrm{~kJ} / \mathrm{mol}$, and that gasoline has an average density of $0.70 \mathrm{~g} / \mathrm{mL}$. The density of ethanol is $0.79 \mathrm{~g} / \mathrm{mL}$. (a) By using the information given as well as data in Appendix C, compare the energy produced by combustion of $1.0 \mathrm{~L}$ of gasoline and of $1.0 \mathrm{~L}$ of ethanol. (b) Assume that the density and heat of combustion of $\mathrm{E} 85$ can be obtained by using $85 \%$ of the values for ethanol and $15 \%$ of the values for gasoline. How much energy could be released by the combustion of $1.0 \mathrm{~L}$ of E85? (c) How many liters of E85 would be needed to provide the same energy as 40 L of gasoline? $(\mathbf{d})$ If gasoline costs $\$ 3.88$ per gallon in the United States, what is the break-even price per gallon of $\mathrm{E} 85$ if the same amount of energy is to be delivered?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 99

The air bags that provide protection in automobiles in the event of an accident expand because of a rapid chemical reaction. From the viewpoint of the chemical reactants as the system, what do you expect for the signs of $q$ and $w$ in this process?

Matthew Bamidele

Matthew Bamidele

Numerade Educator

Problem 100

An aluminum can of a soft drink is placed in a freezer. Later, you find that the can is split open and its contents have frozen. Work was done on the can in splitting it open. Where did the energy for this work come from?

James Irizarry

Numerade Educator

Problem 101

Consider a system consisting of the following apparatus, in which gas is confined in one flask and there is a vacuum in the other flask. The flasks are separated by a valve. Assume that the flasks are perfectly insulated and will not allow the flow of heat into or out of the flasks to the surroundings. When the valve is opened, gas flows from the filled flask to the evacuated one. (a) Is work performed during the expansion of the gas? (b) Why or why not? (c) Can you determine the value of $\Delta E$ for the process?

Matthew Bamidele

Matthew Bamidele

Numerade Educator

Problem 103

The corrosion (rusting) of iron in oxygen-free water includes the formation of iron(II) hydroxide from iron by the following reaction:
$$
\mathrm{Fe}(s)+2 \mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{Fe}(\mathrm{OH})_{2}(s)+\mathrm{H}_{2}(g)
$$
If 1 mol of iron reacts at $298 \mathrm{~K}$ under $101.3 \mathrm{kPa}$ pressure, the reaction performs $2.48 \mathrm{~J}$ of $P-V$ work, pushing back the atmosphere as the gaseous $\mathrm{H}_{2}$ forms. At the same time, $11.73 \mathrm{~kJ}$ of heat is released to the environment. What are the values of $\Delta H$ and of $\Delta E$ for this reaction?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 104

Both oxyhydrogen torches and fuel cells use the following reaction to produce energy:
$$
2 \mathrm{H}_{2}(g)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{H}_{2} \mathrm{O}(l)
$$
Both processes occur at constant pressure. In both cases the change in state of the system is the same: the reactant is oxyhydrogen (“Knallgas") and the product is water. Yet, with an oxyhydrogen torch, the heat evolved is large and with a fuel cell it is small. If heat at constant pressure is considered to be a state function, why does it depend on path?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 105

A sample of gas is contained in a cylinder-and-piston arrangement. There is an external pressure of $100 \mathrm{kPa}$. The gas undergoes the change in state shown in the drawing. (a) Assume first that the cylinder and piston are perfect thermal insulators that do not allow heat to be transferred. What is the value of $q$ for the state change? What is the sign of $w$ for the state change? What can be said about $\Delta E$ for the state change? (b) Now assume that the cylinder and piston are made up of a thermal conductor such as a metal. During the state change, the cylinder gets colder to the touch. What is the sign of $q$ for the state change in this case? Describe the difference in the state of the system at the end of the process in the two cases. What can you say about the relative values of $\Delta E ?$

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 105

A house is designed to have passive solar energy features. Brickwork incorporated into the interior of the house acts as a heat absorber. Each brick weighs approximately $1.8 \mathrm{~kg}$. The specific heat of the brick is $0.85 \mathrm{~J} / \mathrm{g}-\mathrm{K} .$ How many bricks must be incorporated into the interior of the house to provide the same total heat capacity as $1.7 \times 10^{3}$ gal of water?

Matthew Bamidele

Matthew Bamidele

Numerade Educator

Problem 106

A coffee-cup calorimeter of the type shown in Figure 5.18 contains $150.0 \mathrm{~g}$ of water at $25.2^{\circ} \mathrm{C}$. A $200-\mathrm{g}$ block of silver metal is heated to $100.5^{\circ} \mathrm{C}$ by putting it in a beaker of boiling water. The specific heat of $\mathrm{Ag}(s)$ is $0.233 \mathrm{~J} /(\mathrm{g} \cdot \mathrm{K})$. The $\mathrm{Ag}$ is added to the calorimeter, and after some time the contents of the cup reach a constant temperature of $30.2^{\circ} \mathrm{C} .(\mathbf{a})$ Determine the amount of heat, in J, lost by the silver block. (b) Determine the amount of heat gained by the water. The specific heat of water is $4.184 \mathrm{~J} /(\mathrm{g} \cdot \mathrm{K}) .(\mathbf{c})$ The difference between your answers for (a) and (b) is due to heat loss through the Styrofoam $^{\circ}$ cups and the heat necessary to raise the temperature of the inner wall of the apparatus. The heat capacity of the calorimeter is the amount of heat necessary to raise the temperature of the apparatus (the cups and the stopper) by $1 \mathrm{~K} .$ Calculate the heat capacity of the calorimeter in $\mathrm{J} / \mathrm{K}$. (d) What would be the final temperature of the system if all the heat lost by the silver block were absorbed by the water in the calorimeter?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 107

(a) When a 0.47-g sample of benzoic acid is combusted in a bomb calorimeter (Figure 5.19), the temperature rises by $3.284^{\circ} \mathrm{C}$. When a 0.53 -g sample of caffeine, $\mathrm{C}_{8} \mathrm{H}_{10} \mathrm{~N}_{4} \mathrm{O}_{2}$, is burned, the temperature rises by $3.05^{\circ} \mathrm{C}$. Using the value of $26.38 \mathrm{~kJ} / \mathrm{g}$ for the heat of combustion of benzoic acid, calculate the heat of combustion per mole of caffeine at constant volume. (b) Assuming that there is an uncertainty of $0.002^{\circ} \mathrm{C}$ in each temperature reading and that the masses of samples are measured to $0.001 \mathrm{~g},$ what is the estimated uncertainty in the value calculated for the heat of combustion per mole of caffeine?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 108

The corrosion (rusting) of iron in oxygen-free water includes the formation of iron(II) hyrdroxide from iron by the following reaction:
$$
\mathrm{Fe}(s)+2 \mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{Fe}(\mathrm{OH})_{2}(s)+\mathrm{H}_{2}(g)
$$
(a) Calculate the standard enthalpy change for this reaction (the molar enthalpy of formation of $\mathrm{Fe}(\mathrm{OH})_{2}$ is $-583.39 \mathrm{~kJ} / \mathrm{mol})$
(b) Calculate the number of grams of Fe needed to release enough energy to increase the temperature of $250 \mathrm{~mL}$ of water from 22 to $30^{\circ} \mathrm{C}$.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 109

Burning acetylene in oxygen can produce three different carbon-containing products: soot (very fine particles of graphite $), \mathrm{CO}(g),$ and $\mathrm{CO}_{2}(g)$.
(a) Write three balanced equations for the reaction of acetylene gas with oxygen to produce these three products. In each case assume that $\mathrm{H}_{2} \mathrm{O}(l)$ is the only other product.
(b) Determine the standard enthalpies for the reactions in part (a).
(c) Why, when the oxygen supply is adequate, is $\mathrm{CO}_{2}(g)$ the predominant carbon-containing product of the combustion of acetylene?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 110

We can use Hess's law to calculate enthalpy changes that cannot be measured. One such reaction is the conversion of methane to ethane:
$$
2 \mathrm{CH}_{4}(g) \longrightarrow \mathrm{C}_{2} \mathrm{H}_{6}(g)+\mathrm{H}_{2}(g)
$$
Calculate the $\Delta H^{\circ}$ for this reaction using the following thermochemical data:
$$
\begin{aligned}
\mathrm{CH}_{4}(g)+2 \mathrm{O}_{2}(g) & \longrightarrow \mathrm{CO}_{2}(g)+2 \mathrm{H}_{2} \mathrm{O}(l) & \Delta H^{\circ} &=-890.3 \mathrm{~kJ} \\
2 \mathrm{H}_{2}(g)+\mathrm{O}_{2}(g) & \longrightarrow 2 \mathrm{H}_{2} \mathrm{O}(l) & \Delta H^{\circ} &=-571.6 \mathrm{~kJ} \\
2 \mathrm{C}_{2} \mathrm{H}_{6}(g)+7 \mathrm{O}_{2}(g) & \longrightarrow 4 \mathrm{CO}_{2}(g)+6 \mathrm{H}_{2} \mathrm{O}(l) & \Delta H^{\circ} &=-3120.8 \mathrm{~kJ}
\end{aligned}
$$

Nicole Smina

Numerade Educator

Problem 111

From the following data for three prospective fuels, calculate which could provide the most energy per unit mass and per unit volume:

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 112

The hydrocarbons cyclohexane $\left(\mathrm{C}_{6} \mathrm{H}_{12}(l), \Delta H_{f}^{\circ}=-156\right.$
$\mathrm{kJ} / \mathrm{mol}$ ) and 1-hexene $\left(\mathrm{C}_{6} \mathrm{H}_{12}(l), \Delta H_{f}^{\circ}=-74 \mathrm{~kJ} / \mathrm{mol}\right)$ have
the same empirical formula. (a) Calculate the standard enthalpy change for the transformation of cyclohexane to 1-hexene. (b) Which has greater enthalpy, cyclohexane or 1-hexene? (c) Without doing a further calculation and knowing the answer to (b), do you expect cyclohexane or 1-hexene to have the larger combustion enthalpy?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 113

Butane $\mathrm{C}_{4} \mathrm{H}_{10}(l)$ boils at $-0.5^{\circ} \mathrm{C} ;$ at this temperature it has a density of $0.60 \mathrm{~g} / \mathrm{cm}^{3}$. The enthalpy of formation of $\mathrm{C}_{4} \mathrm{H}_{10}(g)$ is $-124.7 \mathrm{~kJ} / \mathrm{mol},$ and the enthalpy of vaporiza-
tion of $\mathrm{C}_{4} \mathrm{H}_{10}(l)$ is $22.44 \mathrm{~kJ} / \mathrm{mol} .$ Calculate the enthalpy change when $1 \mathrm{~L}$ of liquid $\mathrm{C}_{4} \mathrm{H}_{10}(l)$ is burned in air to give $\mathrm{CO}_{2}(g)$ and $\mathrm{H}_{2} \mathrm{O}(g) .$ How does this compare with $\Delta H$ for the complete combustion of $1 \mathrm{~L}$ of liquid methanol, $\mathrm{CH}_{3} \mathrm{OH}(l) ?$ For $\mathrm{CH}_{3} \mathrm{OH}(l),$ the density at $25^{\circ} \mathrm{C}$ is $0.792 \mathrm{~g} / \mathrm{cm}^{3},$ and $\Delta H_{f}^{\circ}=-239 \mathrm{~kJ} / \mathrm{mol}$.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 114

Three hydrocarbons that contain four carbons are listed here, along with their standard enthalpies of formation:
$$
\begin{array}{llc}
\hline \text { Hydrocarbon } & \text { Formula } & \Delta H_{f}^{0}(\mathrm{~kJ} / \mathrm{mol}) \\
\hline \text { Butane } & \mathrm{C}_{4} \mathrm{H}_{10}(g) & -125 \\
\text { 1-Butene } & \mathrm{C}_{4} \mathrm{H}_{8}(g) & -1 \\
\text { 1-Butyne } & \mathrm{C}_{4} \mathrm{H}_{6}(g) & 165 \\
\hline
\end{array}
$$
(a) For each of these substances, calculate the molar enthalpy of combustion to $\mathrm{CO}_{2}(g)$ and $\mathrm{H}_{2} \mathrm{O}(l)$
(b) Calculate the fuel value, in $\mathrm{kJ} / \mathrm{g}$, for each of these compounds.
(c) For each hydrocarbon, determine the percentage of hydrogen by mass.
(d) By comparing your answers for parts (b) and (c), propose a relationship between hydrogen content and fuel value in hydrocarbons.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 115

A $100-\mathrm{kg}$ man decides to add to his exercise routine by walking up six flights of stairs $(30 \mathrm{~m}) 10$ times per day. He figures that the work required to increase his potential energy in this way will permit him to eat an extra order of French fries, at 245 Cal, without adding to his weight. Is he correct in this assumption?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 116

Sucrose $\left(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}\right)$ is produced by plants as follows:
$$
\begin{aligned}
12 \mathrm{CO}_{2}(g)+11 \mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}+12 \mathrm{O}_{2}(g) \\
\Delta H=5645 \mathrm{~kJ}
\end{aligned}
$$
About $4.8 \mathrm{~g}$ of sucrose is produced per day per square meter of the earth's surface. The energy for this endothermic reaction is supplied by the sunlight. About $0.1 \%$ of the sunlight that reaches the earth is used to produce sucrose. Calculate the total energy the sun supplies for each square meter of surface area. Give your answer in kilowatts per square meter $\left(\mathrm{kW} / \mathrm{m}^{2}\right.$ where $\left.1 \mathrm{~W}=1 \mathrm{~J} / \mathrm{s}\right).$

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 117

It is estimated that the net amount of carbon dioxide fixed by photosynthesis on the landmass of Earth is $5.5 \times 10^{16} \mathrm{~g} / \mathrm{yr}$ of $\mathrm{CO}_{2}$. Assume that all this carbon is converted into glucose.
(a) Calculate the energy stored by photosynthesis on land per year, in kJ.
(b) Calculate the average rate of conversion of solar energy into plant energy in megawatts, MW $(1 \mathrm{~W}=1 \mathrm{~J} / \mathrm{s}) .$ A large nuclear power plant produces about $10^{3} \mathrm{MW}$. The energy of how many such nuclear power plants is equivalent to the solar energy conversion?

Matthew Bamidele

Matthew Bamidele

Numerade Educator

Problem 118

At $25^{\circ} \mathrm{C}$ (approximately room temperature) the rms velocity of an Ar atom in air is $1553 \mathrm{~km} / \mathrm{h} .$ (a) What is the rms speed in $\mathrm{m} / \mathrm{s}$ ? (b) What is the kinetic energy (in J) of an Ar atom moving at this speed? (c) What is the total kinetic energy of $1 \mathrm{~mol}$ of Ar atoms moving at this speed?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 119

Suppose an Olympic diver who weighs $52.0 \mathrm{~kg}$ executes a straight dive from a 10 -m platform. At the apex of the dive, the diver is $10.8 \mathrm{~m}$ above the surface of the water. (a) What is the potential energy of the diver at the apex of the dive, relative to the surface of the water? (b) Assuming that all the potential energy of the diver is converted into kinetic energy at the surface of the water, at what speed, in $\mathrm{m} / \mathrm{s}$, will the diver enter the water? (c) Does the diver do work on entering the water? Explain.

Matthew Bamidele

Matthew Bamidele

Numerade Educator

Problem 120

Consider the combustion of a single molecule of $\mathrm{CH}_{4}(g)$, forming $\mathrm{H}_{2} \mathrm{O}(l)$ as a product. (a) How much energy, in J, is produced during this reaction? (b) A typical X-ray light source has an energy of $8 \mathrm{keV}$ (see inside back cover for conversion between $\mathrm{eV}$ and $\mathrm{J}$ ). Is the energy released by the combustion of a $\mathrm{CH}_{4}$ molecule larger or smaller than the energy of an X-ray from this source?

James Irizarry

Numerade Educator

Problem 121

Consider the following unbalanced oxidation-reduction reactions in aqueous solution:
$$
\begin{aligned}
\mathrm{Ag}^{+}(a q)+\mathrm{Li}(s) & \longrightarrow \mathrm{Ag}(s)+\mathrm{Li}^{+}(a q) \\
\mathrm{Fe}(s)+\mathrm{Na}^{+}(a q) & \longrightarrow \mathrm{Fe}^{2+}(a q)+\mathrm{Na}(s) \\
\mathrm{K}(s)+\mathrm{H}_{2} \mathrm{O}(l) & \longrightarrow \mathrm{KOH}(a q)+\mathrm{H}_{2}(g)
\end{aligned}
$$
(a) Balance each of the reactions.
(b) By using data in Appendix $C,$ calculate $\Delta H^{\circ}$ for each of the reactions.
(c) Based on the values you obtain for $\Delta H^{\circ},$ which of the reactions would you expect to be thermodynamically favored?
(d) Use the activity series to predict which of these reactions should occur. ooo (Section 4.4) Are these results in accord with your conclusion in part (c) of this problem?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 122

Consider the following acid-neutralization reactions involving the strong base $\mathrm{NaOH}(a q)$ :
$$
\begin{aligned}
\mathrm{HNO}_{3}(a q)+\mathrm{NaOH}(a q) & \longrightarrow \mathrm{NaNO}_{3}(a q)+\mathrm{H}_{2} \mathrm{O}(l) \\
\mathrm{HCl}(a q)+\mathrm{NaOH}(a q) & \longrightarrow \mathrm{NaCl}(a q)+\mathrm{H}_{2} \mathrm{O}(l) \\
\mathrm{NH}_{4}^{+}(a q)+\mathrm{NaOH}(a q) & \longrightarrow \mathrm{NH}_{3}(a q)+\mathrm{Na}^{+}(a q)+\mathrm{H}_{2} \mathrm{O}(l)
\end{aligned}
$$
(a) By using data in Appendix C, calculate $\Delta H^{\circ}$ for each of the reactions.
(b) As we saw in Section 4.3, nitric acid and hydrochloric acid are strong acids. Write net ionic equations for the neutralization of these acids.
(c) Compare the values of $\Delta H^{\circ}$ for the first two reactions. What can you conclude?
(d) In the third equation $\mathrm{NH}_{4}^{+}(a q)$ is acting as an acid. Based on the value of $\Delta H^{\circ}$ for this reaction, do you think it is a strong or a weak acid? Explain.

James Irizarry

Numerade Educator

Problem 123

Consider two solutions, the first being $50.0 \mathrm{~mL}$ of $1.00 \mathrm{M} \mathrm{CuSO}_{4}$ and the second $50.0 \mathrm{~mL}$ of $2.00 \mathrm{M} \mathrm{KOH} .$
When the two solutions are mixed in a constant-pressure calorimeter, a precipitate forms and the temperature of the mixture rises from 21.5 to $27.7^{\circ} \mathrm{C} .(\mathbf{a})$ Before mixing, how many grams of Cu are present in the solution of $\mathrm{CuSO}_{4}$ ?
(b) Predict the identity of the precipitate in the reaction.
(c) Write complete and net ionic equations for the reaction that occurs when the two solutions are mixed. $(\mathbf{d})$ From the calorimetric data, calculate $\Delta H$ for the reaction that occurs on mixing. Assume that the calorimeter absorbs only a negligible quantity of heat, that the total volume of the solution is $100.0 \mathrm{~mL},$ and that the specific heat and density of the solution after mixing are the same as those of pure water.

Matthew Bamidele

Matthew Bamidele

Numerade Educator

Problem 124

The precipitation reaction between $\mathrm{AgNO}_{3}(a q)$ and $\mathrm{NaCl}(a q)$ proceeds as follows:
$$
\mathrm{AgNO}_{3}(a q)+\mathrm{NaCl}(a q) \longrightarrow \mathrm{NaNO}_{3}(a q)+\operatorname{AgCl}(s)
$$
(a) By using data in Appendix C, calculate $\Delta H^{\circ}$ for the net ionic equation of this reaction.
(b) What would you expect for the value of $\Delta H^{\circ}$ of the overall molecular equation compared to that for the net ionic equation? Explain.
(c) Use the results from (a) and (b) along with data in Appendix C to determine the value of $\Delta H_{f}^{\circ}$ for $\mathrm{AgNO}_{3}(a q)$.

James Irizarry

Numerade Educator

Problem 125

A sample of a hydrocarbon is combusted completely in $\mathrm{O}_{2}(g)$ to produce $21.83 \mathrm{~g} \mathrm{CO}_{2}(g), 4.47 \mathrm{~g} \mathrm{H}_{2} \mathrm{O}(g),$ and $311 \mathrm{~kJ}$ of heat. (a) What is the mass of the hydrocarbon sample that was combusted? (b) What is the empirical formula of the hydrocarbon? (c) Calculate the value of $\Delta H_{f}^{\circ}$ per empiricalformula unit of the hydrocarbon. (d) Do you think that the hydrocarbon is one of those listed in Appendix C? Explain your answer.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 126

The methane molecule, $\mathrm{CH}_{4}$, has the geometry shown in Figure 2.17. Imagine a hypothetical process in which the methane molecule is "expanded," by simultaneously extending all four $\mathrm{C}-\mathrm{H}$ bonds to infinity. We then have the process
$$
\mathrm{CH}_{4}(g) \longrightarrow \mathrm{C}(g)+4 \mathrm{H}(g)
$$
(a) Compare this process with the reverse of the reaction that represents the standard enthalpy of formation of $\mathrm{CH}_{4}(g) .(\mathbf{b})$ Calculate the enthalpy change in each case. Which is the more endothermic process? What accounts for the difference in $\Delta H^{\circ}$ values? (c) Suppose that $3.45 \mathrm{~g}$ $\mathrm{CH}_{4}(g)$ reacts with $1.22 \mathrm{~g} \mathrm{~F}_{2}(g),$ forming $\mathrm{CF}_{4}(g)$ and $\mathrm{HF}(g)$
as sole products. What is the limiting reagent in this reaction? If the reaction occurs at constant pressure, what amount of heat is evolved?

James Irizarry

Numerade Educator

Problem 127

One of the best-selling light, or low-calorie, beers is $4.2 \%$ alcohol by volume and a 355 -mL serving contains 110 Calories; remember: 1 Calorie $=1000 \mathrm{cal}=1 \mathrm{kcal} .$ To estimate the percentage of Calories that comes from the alcohol, consider the following questions. (a) Write a balanced chemical equation for the reaction of ethanol, $\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH},$ with oxygen to make carbon dioxide and water. (b) Use enthalpies of formation in Appendix $\mathrm{C}$ to determine $\Delta H$ for this reaction. $(\mathbf{c})$ If $4.2 \%$ of the total volume is ethanol and the density of ethanol is $0.789 \mathrm{~g} / \mathrm{mL},$ what mass of ethanol does a $355-\mathrm{mL}$ serving of light beer contain? (d) How many Calories are released by the metabolism of ethanol, the reaction from part (a)? (e) What percentage of the 110 Calories comes from the ethanol?

Susan Hallstrom

Susan Hallstrom

Numerade Educator