Chemistry: An Atoms-Focused Approach

Thomas R. Gilbert, Rein V. Kirss, Natalie Foster

Chapter 9

Thermochemistry: Energy Changes in Chemical Reactions - all with Video Answers

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Chapter Questions

Problem 1

Figure P9.1 shows the compression stroke of a diesel engine. How does upward motion of the piston alter the internal energy of the gases trapped in the cylinder? (FIGURE CAN'T COPY)

Jake Rempel

Jake Rempel

Numerade Educator

Problem 2

Figure P9.2 shows the power stroke of a diesel engine as energy released by the rapid combustion of the air and fuel vapor inside the cylinder pushes the cylinder downward. If the gases inside the cylinder are a thermodynamic system, how does the internal energy of the system change as a result of the combustion reaction and downward motion of the piston? In your description indicate the signs on $\Delta E, q,$ and $w$. (FIGURE CAN'T COPY)

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 3

Based on their molecular structures, predict which of the four hydrocarbons in Figure P9.3 has the highest fuel value and which has the lowest. (FIGURE CAN'T COPY)

Angelos Evangelinos

Angelos Evangelinos

Numerade Educator

Problem 4

The diagram in Figure P9.4 shows how the volume of a reaction mixture at constant pressure and temperature changes as $\mathrm{N}_{2}$ and $\mathrm{H}_{2}$ combine, forming $\mathrm{NH}_{3}$.
a. In this reaction, does the reaction mixture do work on the surroundings, or vice versa?
b. Use data from Appendix 4 to calculate $\Delta H_{\text {rxn }}^{\circ}$ for the formation of one mole of product.
c. To achieve a final temperature that is the same as the initial one, does heat flow out from, or into, the reaction mixture?
(FIGURE CAN'T COPY)

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 5

Assuming the reaction mixture in Figure P9.4 is a thermodynamic system, what are the signs on $q, w,$ and $\Delta E ?$ If each molecule in the figure represents one mole of reactant or product, what is the percent yield of the reaction?

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 6

The diagram in Figure $\mathrm{P} 9.6$ is based on the standard heats of formation $\left(\Delta H_{f}^{\circ}\right)$ values for four compounds made from the elements listed on the "zero" line of the vertical axis. (FIGURE CAN'T COPY)
a. Why are the elements all on the same horizontal line?
b. Why is $\mathrm{C}_{2} \mathrm{H}_{2}(g)$ sometimes called an "endothermic" compound?
c. Based on these $\Delta H_{\mathrm{f}}^{\circ}$ values, predict which of these two reactions has the more negative enthalpy change: $$2 \mathrm{C}_{2} \mathrm{H}_{2}(g)+3 \mathrm{O}_{2}(g) \rightarrow 4 \mathrm{CO}(g)+2 \mathrm{H}_{2} \mathrm{O}(g)$$ or $$2 \mathrm{C}_{2} \mathrm{H}_{2}(g)+5 \mathrm{O}_{2}(g) \rightarrow 4 \mathrm{CO}_{2}(g)+2 \mathrm{H}_{2} \mathrm{O}(g)$$

Ronald Prasad

Numerade Educator

Problem 7

Figure $\mathrm{P} 9.7$ represents a chemical reaction taking place at constant temperature and pressure.
a. Write a balanced chemical equation for the reaction.
b. Use data from Appendix 4 to calculate $\Delta H_{\mathrm{rxn}}^{\circ}$ for the formation of one mole of CO.
c. To achieve a final temperature that is the same as the initial one, does heat flow out from, or into, the reaction mixture?
(FIGURE CAN'T COPY)

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 8

Use representations [A] through [I] in Figure P9.8 to answer questions a-f.
a. Match two of the particulate images to the phase change for liquid nitrogen in [B].
b. Match two of the particulate images to the phase change for dry ice (solid $\mathrm{CO}_{2}$ ) in $[\mathrm{H}]$.
c. Which, if any, of the photos correspond to [D]? Are these endothermic or exothermic?
d. Which, if any, of the photos correspond to $[\mathrm{F}]$ ? Are these endothermic or exothermic?
e. What bonds break when the solid ammonium nitrate in [E] dissolves in water to activate the cold pack?
f. Which particulate images show an element or compound in its standard state?
(FIGURE CAN'T COPY)

Allea Cauilan

Numerade Educator

Problem 9

How are energy and work related?

David Collins

Numerade Educator

Problem 10

Explain the difference between potential energy and kinetic energy in molecules.

Angelos Evangelinos

Angelos Evangelinos

Numerade Educator

Problem 11

Explain what is meant by a state function.

David Collins

Numerade Educator

Problem 12

Are kinetic energy and potential energy both state functions?

David Collins

Numerade Educator

Problem 13

If the potential energy of a particle increases as it is moved away from another particle, do the two particles attract or repel each other?

Angelos Evangelinos

Angelos Evangelinos

Numerade Educator

Problem 14

Explain how there can be kinetic energy in a stationary ice cube.

Angelos Evangelinos

Angelos Evangelinos

Numerade Educator

Problem 15

Describe two ways to increase the internal energy of a gas sample.

Angelos Evangelinos

Angelos Evangelinos

Numerade Educator

Problem 16

Assuming the kernels of unpopped popcorn in Figure P9.16 constitute a thermodynamic system, what are the signs of $q$ $w,$ and $\Delta E$ during the popping process? (FIGURE CAN'T COPY)

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 17

How can the product of pressure and volume ( $P-V$ work) have energy units?

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 18

Why is there a negative sign in front of the $P \Delta V$ term in $\Delta E=q-P \Delta V ?$

Angelos Evangelinos

Angelos Evangelinos

Numerade Educator

Problem 19

Which of the following processes are exothermic, and which are endothermic?
a. Molten aluminum solidifies.
b. Rubbing alcohol evaporates from the skin.
c. Fog forms over San Francisco Bay.

Angelos Evangelinos

Angelos Evangelinos

Numerade Educator

Problem 20

Which of the following processes are exothermic, and which are endothermic?
a. Ice cubes solidify in the freezer.
b. Ice cubes in a frost-free freezer slowly lose mass.
c. Dew forms on a lawn overnight.

Angelos Evangelinos

Angelos Evangelinos

Numerade Educator

Problem 21

What happens to the internal energy of a liquid at its boiling point when it vaporizes?

David Collins

Numerade Educator

Problem 22

What happens to the internal energy of a gas when it expands (with no heat flow)?

David Collins

Numerade Educator

Problem 23

How much $P-V$ work does a gas system do on its surroundings at a constant pressure of 1.00 atm if the volume of gas triples from $250.0 \mathrm{mL}$ to $750.0 \mathrm{mL}$ ? Express your answer in $\mathrm{L} \cdot$ atm and joules $(\mathrm{J})$.

David Collins

Numerade Educator

Problem 24

An expanding gas does $150.0 \mathrm{J}$ of work on its surroundings at a constant pressure of 1.01 atm. If the gas initially occupied $68 \mathrm{mL},$ what is the final volume of the gas?

David Collins

Numerade Educator

Problem 25

Calculate $\Delta E$ when
a. $q=100.0 \mathrm{J} ; w=-50.0 \mathrm{J}$
b. $q=6.2 \mathrm{kJ} ; w=0.70 \mathrm{L} \cdot$ atm
c. $q=-615 \mathrm{kJ} ; w=-3.25$ kilowatt-hours $(1 \mathrm{kWh}=$ $3600 \mathrm{kJ})$

Angelos Evangelinos

Angelos Evangelinos

Numerade Educator

Problem 26

Calculate $\Delta E$ for a system that absorbs $726 \mathrm{kJ}$ of heat from its surroundings and does $526 \mathrm{kJ}$ of work on its surroundings.

Angelos Evangelinos

Angelos Evangelinos

Numerade Educator

Problem 27

Calculate $\Delta E$ for the combustion of a gas that releases $210.0 \mathrm{kJ}$ of heat to its surroundings and does $65.5 \mathrm{kJ}$ of work on its surroundings.

Angelos Evangelinos

Angelos Evangelinos

Numerade Educator

Problem 28

Calculate $\Delta E$ for a chemical reaction that releases $90.7 \mathrm{kJ}$ of heat to its surroundings but does no work on them.

Angelos Evangelinos

Angelos Evangelinos

Numerade Educator

Problem 29

The following reactions take place in a cylinder equipped with a movable piston at atmospheric pressure (Figure P9.29). Which reactions will result in work being done on the surroundings? What is the sign of $w ?$ Assume the system returns to an initial temperature of $110^{\circ} \mathrm{C} .$ Hint: The volume of a gas is proportional to the number of moles ( $n$ ) at constant temperature and pressure.
a. $\mathrm{CH}_{4}(g)+2 \mathrm{O}_{2}(g) \rightarrow \mathrm{CO}_{2}(g)+2 \mathrm{H}_{2} \mathrm{O}(g)$
b. $C_{3} H_{8}(g)+5 O_{2}(g) \rightarrow 3 C O_{2}(g)+4 H_{2} O(g)$
c. $\mathrm{N}_{2}(g)+2 \mathrm{O}_{2}(g) \rightarrow 2 \mathrm{NO}_{2}(g)$
(FIGURE CAN'T COPY)

David Collins

Numerade Educator

Problem 30

In which direction will the piston described in Problem 9.29 move when the following reactions are carried out at atmospheric pressure inside the cylinder and after the system has returned to its initial temperature of $110^{\circ} \mathrm{C} ?$ What is the sign on w? Hint: The volume of a gas is proportional to the number of moles ( $n$ ) at constant temperature and pressure.
a. $\mathrm{N}_{2}(g)+3 \mathrm{H}_{2}(g) \rightarrow 2 \mathrm{NH}_{3}(g)$
b. $C(s)+O_{2}(g) \rightarrow C O_{2}(g)$
c. $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}(g)+3 \mathrm{O}_{2}(g) \rightarrow 2 \mathrm{CO}_{2}(g)+3 \mathrm{H}_{2} \mathrm{O}(g)$

Lottie Adams

Numerade Educator

Problem 31

What is meant by an entbalpy change?

David Collins

Numerade Educator

Problem 32

Describe the difference between an internal energy change $(\Delta E)$ and an enthalpy change $(\Delta H)$.

David Collins

Numerade Educator

Problem 33

Why is the sign of $\Delta H$ negative for an exothermic process?

Angelos Evangelinos

Angelos Evangelinos

Numerade Educator

Problem 34

What happens to the magnitude and sign of the enthalpy change when a process is reversed?

Angelos Evangelinos

Angelos Evangelinos

Numerade Educator

Problem 35

Adding Drano to a clogged sink causes the drainpipe to get warm. What is the sign of $\Delta H$ when Drano dissolves in water?

Angela Williamson

Angela Williamson

Numerade Educator

Problem 36

Breaking the small pouch of water inside a chemical cold pack containing ammonium nitrate activates the pack, which is used by sports trainers for injured athletes. What is the sign of $\Delta H$ for the process taking place in the cold pack?

Angelos Evangelinos

Angelos Evangelinos

Numerade Educator

Problem 37

The stable form of oxygen at room temperature and pressure is the diatomic molecule $\mathrm{O}_{2} .$ What is the sign of $\Delta H$ for the following process? $$\mathrm{O}_{2}(g) \rightarrow 2 \mathrm{O}(g)$$

David Collins

Numerade Educator

Problem 38

Gypsum is the common name of calcium sulfate dihydrate which has the formula $\mathrm{CaSO}_{4} \cdot 2 \mathrm{H}_{2} \mathrm{O}$ When gypsum is heated to $150^{\circ} \mathrm{C},$ it loses most of the water in its formula and forms plaster of Paris $\left(\mathrm{CaSO}_{4} \cdot 0.5 \mathrm{H}_{2} \mathrm{O}\right):$ $2 \mathrm{CaSO}_{4} \cdot 2 \mathrm{H}_{2} \mathrm{O}(s) \rightarrow 2 \mathrm{CaSO}_{4} \cdot 0.5 \mathrm{H}_{2} \mathrm{O}(s)+3 \mathrm{H}_{2} \mathrm{O}(g)$ What is the sign of $\Delta H$ for making plaster of Paris from gypsum?

David Collins

Numerade Educator

Problem 39

A solid with metallic properties is formed when hydrogen gas is compressed under extremely high pressures. What is the sign of $\Delta H$ for the deposition process: $\mathrm{H}_{2}(g) \rightarrow \mathrm{H}_{2}(s) ?$

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 40

In a simple "kitchen chemistry" experiment, some vinegar is poured into an empty soda bottle. A deflated balloon containing baking soda is stretched over the mouth of the bottle. Holding up the balloon and shaking it allows the baking soda to fall into the vinegar, which starts the following reaction and inflates the balloon: $$\begin{aligned} \mathrm{NaHCO}_{3}(a q)+\mathrm{CH}_{3} \mathrm{COOH}(a q) \rightarrow & \\ & \mathrm{CH}_{3} \mathrm{COONa}(a q)+\mathrm{CO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(\ell) \end{aligned}$$ If the contents of the bottle are the system, is work being done on the surroundings or on the system?

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 41

What is the difference between specific beat and beat capacity?

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 42

Which has more heat capacity: one liter of water or one cubic meter of water? Which has more molar heat capacity?

Angelos Evangelinos

Angelos Evangelinos

Numerade Educator

Problem 43

Why is the heat of vaporization of water so much greater than its heat of fusion?

Angelos Evangelinos

Angelos Evangelinos

Numerade Educator

Problem 44

Figure P9.44 shows portions of the heating curves for two moles each of three liquids: chloroform (bp $142^{\circ} \mathrm{C}$ ), water $\left(\text { bp } 100^{\circ} \mathrm{C}\right),$ and ethanol $\left(\mathrm{bp} 78^{\circ} \mathrm{C}\right) .$ Rank the liquids in order of their molar enthalpies of vaporization from lowest
to highest. (FIGURE CAN'T COPY)

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 45

In Figure $\mathrm{P} 9.44,$ why do line segments $\overline{A B}$ have slightly different slopes in each curve?

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 46

The same quantity of heat warms equal masses of metals $\mathrm{A}$ and B. Does the metal with the larger specific heat reach the higher temperature?

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 47

Most automobile engines are cooled by water circulating through them and a radiator. However, the original Volkswagen Beetle had an air-cooled engine. Why might car designers choose water cooling over air cooling?

David Collins

Numerade Educator

Problem 48

The reactor-core cooling systems in some nuclear power plants use liquid sodium as the coolant. Sodium has a thermal conductivity of $1.42 \mathrm{J} /(\mathrm{cm} \cdot \mathrm{s} \cdot \mathrm{K}),$ which is quite high compared with that of water $\left[6.1 \times 10^{-3} \mathrm{J} /(\mathrm{cm} \cdot \mathrm{s} \cdot \mathrm{K})\right] .$ The respective molar heat capacities are $28.3 \mathrm{J} /(\mathrm{mol} \cdot \mathrm{K})$ and $75.3 \mathrm{kJ} /(\mathrm{mol} \cdot \mathrm{K})$. What is the advantage of using liquid sodium over water in this application?

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 49

How much heat must be absorbed by $100.0 \mathrm{g}$ of water to raise its temperature from $30.0^{\circ} \mathrm{C}$ to $100.0^{\circ} \mathrm{C} ?$

Angelos Evangelinos

Angelos Evangelinos

Numerade Educator

Problem 50

At an elevation where the boiling point of water is $93^{\circ} \mathrm{C}$ $1.33 \mathrm{kg}$ of water at $30^{\circ} \mathrm{C}$ absorbs $290.0 \mathrm{kJ}$ from a mountain climber's stove. Is this amount of thermal energy sufficient to heat the water to its boiling point?

Angelos Evangelinos

Angelos Evangelinos

Numerade Educator

Problem 51

Use the following data to sketch a heating curve for one mole of methanol. Start the curve at $-100^{\circ} \mathrm{C}$ and end it at $100^{\circ} \mathrm{C}$.
$$\begin{array}{ll}\hline \text { Boiling point } & 65^{\circ} \mathrm{C} \\\hline \text { Melting point } & -94^{\circ} \mathrm{C} \\\hline \text { Heat of vaporization } & 35.3 \mathrm{kJ} / \mathrm{mol} \\\hline \text { Heat of fusion }\left(\Delta \mathrm{H}_{\text {fus }}\right) & 3.18 \mathrm{kJ} / \mathrm{mol} \\\hline \text { Molar heat capacity }(\ell) & 81.1 \mathrm{J} /\left(\mathrm{mol} \cdot^{\circ} \mathrm{C}\right) \\\hline \text { Molar heat capacity }(g) & 43.9 \mathrm{J} /\left(\mathrm{mol} \cdot^{\circ} \mathrm{C}\right) \\\hline \text { Molar heat capacity }(\mathrm{s}) & 48.7 \mathrm{J} /\left(\mathrm{mol} \cdot^{\circ} \mathrm{C}\right) \\\hline\end{array}$$

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 52

Use the following data to sketch a heating curve for 1.5 moles of acetic acid. Start the curve at $+16^{\circ} \mathrm{C}$ and end it at $130^{\circ} \mathrm{C}$.
$$\begin{array}{ll}\hline \text { Boiling point } & 118^{\circ} \mathrm{C} \\\hline \text { Melting point } & 16^{\circ} \mathrm{C} \\\hline \text { Heat of vaporization } & 23.7 \mathrm{kJ} / \mathrm{mol} \\\hline \text { Heat of fusion }\left(\Delta H_{\text {fus }}\right) & 11.7 \mathrm{kJ} / \mathrm{mol} \\\hline \text { Molar heat capacity }(\ell) & 123.1 \mathrm{J} /\left(\mathrm{mol} \cdot^{\circ} \mathrm{C}\right) \\\hline \text { Molar heat capacity }(g) & 63.4 \mathrm{J} /\left(\mathrm{mol} \cdot^{\circ} \mathrm{C}\right) \\\hline\end{array}$$

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 53

During a strenuous workout, an athlete generates $233 \mathrm{kJ}$ of thermal energy. What mass of water would have to evaporate from the athlete's skin to dissipate this energy?

Angelos Evangelinos

Angelos Evangelinos

Numerade Educator

Problem 54

The same quantity of thermal energy is added to equal masses of titanium, iron, silver, and lead. All of them are initially at the same temperature. Which metal has the highest final temperature?

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 55

Exactly $10.0 \mathrm{mL}$ of water at $25.0^{\circ} \mathrm{C}$ is added to a hot iron skillet. All of the water is converted into steam at $100.0^{\circ} \mathrm{C}$ The mass of the pan is $1.20 \mathrm{kg} .$ What is the change in temperature of the skillet?

Angelos Evangelinos

Angelos Evangelinos

Numerade Educator

Problem 56

A $20.0 \mathrm{g}$ piece of iron and a $20.0 \mathrm{g}$ piece of gold at $100.0^{\circ} \mathrm{C}$ are dropped into $1.00 \mathrm{L}$ of water at $20.0^{\circ} \mathrm{C} .$ What is the final temperature of the water and the pieces of metal?

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 57

Why is it necessary to know the heat capacity of a calorimeter?

David Collins

Numerade Educator

Problem 58

Could an endothermic reaction be used to determine the heat capacity of a calorimeter?

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 59

If we replace the water in a bomb calorimeter with another liquid, do we need to determine a new heat capacity of the calorimeter?

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 60

When measuring the heat of combustion of a very small amount of material, would you prefer to use a calorimeter having a heat capacity that is small or large?

Angelos Evangelinos

Angelos Evangelinos

Numerade Educator

Problem 61

Calculate the heat capacity of a calorimeter if the combustion of $5.000 \mathrm{g}$ of benzoic acid produces a temperature increase of $16.397^{\circ} \mathrm{C}$.

Angelos Evangelinos

Angelos Evangelinos

Numerade Educator

Problem 62

Calculate the heat capacity of a calorimeter if the combustion of $4.663 \mathrm{g}$ of benzoic acid produces an increase in temperature of $7.149^{\circ} \mathrm{C}$.

Angelos Evangelinos

Angelos Evangelinos

Numerade Educator

Problem 63

The complete combustion of $1.200 \mathrm{g}$ of cinnamaldehyde $(\mathrm{C}_{9} \mathrm{H}_{8} \mathrm{O},$ one of the compounds in cinnamon) in a bomb. calorimeter $\left(C_{\text {calorimeter }}=3.640 \mathrm{kJ} /^{\circ} \mathrm{C}\right)$ produced an increase in temperature of $12.79^{\circ} \mathrm{C} .$ How much thermal energy is produced during the complete combustion of one mole of cinnamaldehyde?

Angelos Evangelinos

Angelos Evangelinos

Numerade Educator

Problem 64

Spices The aromatic hydrocarbon cymene $\left(\mathrm{C}_{10} \mathrm{H}_{14}\right)$ is found in nearly 100 spices and fragrances, including coriander, anise, and thyme. The complete combustion of $1.608 \mathrm{g}$ of cymene in a bomb calorimeter $\left(C_{\text {calorimeter }}=3.640 \mathrm{kJ} /^{\circ} \mathrm{C}\right)$ produced an increase in temperature of $19.35^{\circ} \mathrm{C} .$ How much thermal energy is produced during the complete combustion of one mole of cymene?

Angelos Evangelinos

Angelos Evangelinos

Numerade Educator

Problem 65

Hormone Mimics Phthalates that are used to make plastics flexible are among the most abundant industrial contaminants in the environment. Several have been shown to act as hormone mimics in humans by activating the receptors for estrogen, a female sex hormone. Combustion of one mole of one of these compounds, dimethyl phthalate $\left(\mathrm{C}_{10} \mathrm{H}_{10} \mathrm{O}_{4}\right),$ produces $4685 \mathrm{kJ}$ of thermal energy. If $1.00 \mathrm{g}$
of dimethyl phthalate is combusted in a bomb calorimeter whose heat capacity ( $C_{\text {calorimeter }}$ ) is $7.854 \mathrm{kJ} /^{\circ} \mathrm{C},$ what is the change in temperature of the calorimeter?

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 66

The flavor of anise is due to anethole, a compound with the molecular formula $\mathrm{C}_{10} \mathrm{H}_{12} \mathrm{O}$ Combustion of one mole of anethole produces $5541 \mathrm{kJ}$ of thermal energy. If $0.950 \mathrm{g}$ of anethole is combusted in a bomb calorimeter whose heat capacity ( $C_{\text {calorimeter }}$ ) is $7.854 \mathrm{kJ} /^{\circ} \mathrm{C},$ what is the change in temperature of the calorimeter?

Angelos Evangelinos

Angelos Evangelinos

Numerade Educator

Problem 67

A coffee-cup calorimeter contains $100.0 \mathrm{mL}$ of $1.00 M \mathrm{HCl}$ at $22.4^{\circ} \mathrm{C} .$ When $0.243 \mathrm{g}$ of $\mathrm{Mg}$ metal is added to the acid, the ensuing reaction: $$\mathrm{Mg}(s)+2 \mathrm{HCl}(a q) \rightarrow \mathrm{MgCl}_{2}(a q)+\mathrm{H}_{2}(g) \quad \Delta H_{\mathrm{rxn}}=?$$ causes the temperature of the solution to increase to $33.4^{\circ} \mathrm{C}$ What is the value of $\Delta H_{\mathrm{rxn}}$ of the reaction? Assume the density of the solution is $1.01 \mathrm{g} / \mathrm{mL}$ and that its specific heat is $4.18 \mathrm{J} /\left(\mathrm{g} \cdot^{\circ} \mathrm{C}\right)$.

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 68

When $4.00 \mathrm{g} \mathrm{NH}_{4} \mathrm{NO}_{3}(\mathscr{M}=80.04 \mathrm{g} /$mol) - the active ingredient in some chemical cold packs is dissolved in $96.0 \mathrm{g} \mathrm{H}_{2} \mathrm{O},$ the temperature of the resulting solution is $3.07^{\circ} \mathrm{C}$ colder than the water and ammonium nitrate were before they were mixed together. What is the value of $\Delta H$ for the following dissolution process? $$\mathrm{NH}_{4} \mathrm{NO}_{3}(s) \rightarrow \mathrm{NH}_{4} \mathrm{NO}_{3}(a q) \quad \Delta H=?$$

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 69

How is Hess's law consistent with the law of conservation of energy?

David Collins

Numerade Educator

Problem 70

Would Hess's law be valid if enthalpy were not a state function? Why or why not?

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 71

Use the $\Delta H_{\mathrm{rxn}}^{\circ}$ values of the following reactions:
$$\begin{aligned}2 \mathrm{SO}_{2}(g)+\mathrm{O}_{2}(g) & \rightarrow 2 \mathrm{SO}_{3}(g) & \Delta H_{\mathrm{rsn}}^{\circ} &=-196 \mathrm{kJ} \\\frac{1}{4} \mathrm{S}_{8}(s)+3 \mathrm{O}_{2}(g) & \rightarrow 2 \mathrm{SO}_{3}(g) & \Delta H_{\mathrm{rxn}}^{\circ} &=-790 \mathrm{kJ}\end{aligned}$$
to calculate the $\Delta H_{\mathrm{rxn}}^{\circ}$ value of this reaction: $$\frac{1}{8} \mathrm{S}_{\mathrm{g}}(s)+\mathrm{O}_{2}(g) \rightarrow \mathrm{SO}_{2}(g) \quad \Delta H_{\mathrm{ran}}^{\circ}=?$$

Angelos Evangelinos

Angelos Evangelinos

Numerade Educator

Problem 72

The destruction of the ozone layer by chlorofluorocarbons (CFCs) can be described by the following reactions:
$$\begin{aligned}\mathrm{ClO}(g)+\mathrm{O}_{3}(g) & \rightarrow \mathrm{Cl}(g)+2 \mathrm{O}_{2}(g) & \Delta H_{\mathrm{rxn}}^{\circ} &=-29.90 \mathrm{kJ} \\2 \mathrm{O}_{3}(g) \rightarrow 3 \mathrm{O}_{2}(g) & & \Delta H_{\mathrm{rxn}}^{\circ} &=+24.18 \mathrm{kJ}\end{aligned}$$ Use the preceding $\Delta H_{\mathrm{rxn}}^{\circ}$ values to determine the value of the standard heat of reaction for this reaction: $$\mathrm{Cl}(g)+\mathrm{O}_{3}(g) \rightarrow \mathrm{ClO}(g)+\mathrm{O}_{2}(g) \quad \Delta H_{\mathrm{rxn}}^{\circ}=?$$

Angelos Evangelinos

Angelos Evangelinos

Numerade Educator

Problem 73

The mineral spodumene $\left(\operatorname{LiAlSi}_{2} \mathrm{O}_{6}\right)$ exists in two crystalline forms called $\alpha$ and $\beta .$ Use Hess's law and the following information to calculate $\Delta H_{\mathrm{rxn}}^{\circ}$ for the conversion of $\alpha$ -spodumene into $\beta$ -spodumene: $$\begin{array}{r}\mathrm{Li}_{2} \mathrm{O}(s)+2 \mathrm{Al}(s)+4 \mathrm{SiO}_{2}(s)+\frac{3}{2} \mathrm{O}_{2}(g) \rightarrow 2 \alpha-\mathrm{LiAlSi}_{2} \mathrm{O}_{6}(s) \\ \Delta H_{\mathrm{rxn}}^{\circ}=-1870.6 \mathrm{kJ} \end{array}$$ $$\begin{array}{r}\mathrm{Li}_{2} \mathrm{O}(s)+2 \mathrm{Al}(s)+4 \mathrm{SiO}_{2}(s)+\frac{3}{2} \mathrm{O}_{2}(g) \rightarrow 2 \beta-\mathrm{LiAlSi}_{2} \mathrm{O}_{6}(s) \\\Delta H_{\mathrm{rxn}}^{\circ}=-1814.6 \mathrm{kJ} \end{array}$$

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 74

Use the following data to determine whether the conversion of diamond into graphite is exothermic or endothermic:
$$\begin{array}{ll}\mathrm{C}(s, \text { diamond })+\mathrm{O}_{2}(g) \rightarrow \mathrm{CO}_{2}(g) & \Delta H_{\mathrm{rm}}^{\circ}=-395.4 \mathrm{kJ} \\2 \mathrm{CO}(g)+\mathrm{O}_{2}(g) \rightarrow 2 \mathrm{CO}_{2}(g) & \Delta H_{\mathrm{rsn}}^{\circ}=-566.0 \mathrm{kJ}\end{array}$$ $$\begin{aligned} &2 \mathrm{CO}(g) \rightarrow \mathrm{C}(s, \text { graphite })+\mathrm{CO}_{2}(g) \quad \Delta H_{\mathrm{rxn}}^{\circ}=-172.5 \mathrm{kJ}\\
&\mathrm{C}(s, \text { diamond }) \rightarrow \mathrm{C}(s, \text { graphite }) \quad \Delta H_{\mathrm{ran}}^{\circ}=?
\end{aligned}$$

David Collins

Numerade Educator

Problem 75

Given the following thermochemical data: $$\begin{array}{ll}\frac{1}{2} \mathrm{N}_{2}(g)+\frac{1}{2} \mathrm{O}_{2}(g) \rightarrow \frac{1}{2} \mathrm{NO}(g) & \Delta H_{\mathrm{rxn}}^{\circ}=+90.3 \mathrm{kJ} \\ \mathrm{NO}(g)+\frac{1}{2} \mathrm{Cl}_{2}(g) \rightarrow \mathrm{NOCl}(g) & \Delta H_{\mathrm{rxn}}^{\circ}=-38.6 \mathrm{kJ} \end{array}$$ what is the value of $\Delta H_{\mathrm{rxn}}^{\circ}$ for the decomposition of NOCl? $$2 \mathrm{NOCl}(g) \rightarrow \mathrm{N}_{2}(g)+\mathrm{O}_{2}(g)+\mathrm{Cl}_{2}(g) \quad \Delta H_{\mathrm{rxn}}^{\circ}=?$$

Angelos Evangelinos

Angelos Evangelinos

Numerade Educator

Problem 76

Synthetic natural gas (SNG), sometimes called substitute natural gas, is a methane-containing mixture produced from the gasification of coal or oil shale directly at the site of the mine or oil field. One reaction for the production of SNG is: $$4 \mathrm{CO}(g)+8 \mathrm{H}_{2}(g) \rightarrow 3 \mathrm{CH}_{4}(g)+\mathrm{CO}_{2}(g)+2 \mathrm{H}_{2} \mathrm{O}(g)$$ Use the following thermochemical equations to determine $\Delta H^{\circ}$ for the reaction as written.
$$\begin{aligned}\mathrm{C}(\text { graphite })+2 \mathrm{H}_{2}(g) & \rightarrow \mathrm{CH}_{4}(g) & \Delta H^{\circ} &=-74.8 \mathrm{kJ} \\\mathrm{C}(\text { graphite })+\frac{1}{2} \mathrm{O}_{2}(g) & \rightarrow \mathrm{CO}(g) & \Delta H^{\circ} &=-110.5 \mathrm{kJ}\end{aligned}$$ $$\begin{array}{ll}\mathrm{CO}(g)+\frac{1}{2} \mathrm{O}_{2}(g) \rightarrow \mathrm{CO}_{2}(g) & \Delta H^{\circ}=-283.0 \mathrm{kJ} \\\mathrm{H}_{2}(g)+\frac{1}{2} \mathrm{O}_{2}(g) \rightarrow \mathrm{H}_{2} \mathrm{O}(g) & \Delta H^{\circ}=-285.8 \mathrm{kJ}\end{array}$$

Angelos Evangelinos

Angelos Evangelinos

Numerade Educator

Problem 77

Why is the standard heat of formation of $\mathrm{CO}(g)$ difficult to measure experimentally?

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 78

Explain how the use of $\Delta H_{f}^{\circ}$ to calculate $\Delta H_{\mathrm{rxn}}^{\circ}$ is an example of Hess's law.

David Collins

Numerade Educator

Problem 79

Oxygen and ozone are both forms of elemental oxygen. Are the standard heats of formation of oxygen and ozone the same? Why or why not?

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 80

Why are the standard heats of formation of elements in their standard states assigned a value of zero?

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 81

Why must the stoichiometry of a reaction be known in order to estimate the enthalpy change from bond energies?

Sam Limsuwannarot

Sam Limsuwannarot

Numerade Educator

Problem 82

Why must the structures of the reactants and products be known in order to estimate the enthalpy change of a reaction from bond energies?

Sam Limsuwannarot

Sam Limsuwannarot

Numerade Educator

Problem 83

When calculating the enthalpy change for a chemical reaction using bond energies, why is it important that the reactants and products all be gases?

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 84

If the energy needed to break two moles of $\mathrm{C}=\mathrm{O}$ bonds is greater than the sum of the energies needed to break the $\mathrm{O}=\mathrm{O}$ bonds in one mole of $\mathrm{O}_{2}$ and vaporize one mole of carbon, why does the combustion of pure carbon release heat?

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 85

For which of the following reactions does $\Delta H_{\mathrm{rxn}}^{\circ}$ represent a heat of formation?
a. $\mathrm{C}(s)+\frac{1}{2} \mathrm{O}_{2}(g) \rightarrow \mathrm{CO}(g)$
b. $6 \mathrm{MnO}(s)+\mathrm{O}_{2}(g) \rightarrow 2 \mathrm{Mn}_{3} \mathrm{O}_{4}(s)$
c. $2 \mathrm{Na}(s)+\mathrm{C}(s, \text { graphite })+3 / 2 \mathrm{O}_{2}(g) \rightarrow \mathrm{Na}_{2} \mathrm{CO}_{3}(s)$
d. $4 \mathrm{H}_{2}(g)+2 \mathrm{C}(s) \rightarrow 2 \mathrm{CH}_{4}(g)$

Angelos Evangelinos

Angelos Evangelinos

Numerade Educator

Problem 86

For which of the following reactions does $\Delta H_{\mathrm{rxn}}^{\circ}$ also represent a heat of formation?
a. $2 \mathrm{N}_{2}(g)+3 \mathrm{O}_{2}(g) \rightarrow 2 \mathrm{NO}_{2}(g)+2 \mathrm{NO}(g)$
b. $\mathrm{N}_{2}(g)+\mathrm{O}_{2}(g) \rightarrow 2 \mathrm{NO}(g)$
c. $2 \mathrm{NO}_{2}(g) \rightarrow \mathrm{N}_{2} \mathrm{O}_{4}(g)$
d. $\mathrm{N}_{2}(g)+2 \mathrm{O}_{2}(g) \rightarrow 2 \mathrm{NO}_{2}(g)$

Angelos Evangelinos

Angelos Evangelinos

Numerade Educator

Problem 87

Use standard heats of formation from Appendix 4 to calculate the standard heat of reaction for the following methane-generating reaction of methanogenic bacteria: $$4 \mathrm{H}_{2}(g)+\mathrm{CO}_{2}(g) \rightarrow \mathrm{CH}_{4}(g)+2 \mathrm{H}_{2} \mathrm{O}(\ell)$$

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 88

Use standard enthalpies of formation from Appendix 4 to calculate the standard enthalpy of reaction for the following methane-generating reaction of methanogenic bacteria, given $\Delta H_{f}^{\circ}$ of $\mathrm{CH}_{3} \mathrm{NH}_{2}(g)=-22.97 \mathrm{kJ} / \mathrm{mol}:$ $$4 \mathrm{CH}_{3} \mathrm{NH}_{2}(g)+2 \mathrm{H}_{2} \mathrm{O}(\ell) \rightarrow 3 \mathrm{CH}_{4}(g)+\mathrm{CO}_{2}(g)+4 \mathrm{NH}_{3}(g)$$

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 89

Ammonium nitrate decomposes to $\mathrm{N}_{2} \mathrm{O}$ and water vapor at temperatures between $250^{\circ} \mathrm{C}$ and $300^{\circ} \mathrm{C} .$ Write a balanced chemical reaction describing the decomposition of ammonium nitrate, and calculate its $\Delta H_{\mathrm{rxn}}^{\circ}$ using the appropriate $\Delta H_{\mathrm{f}}^{\circ}$ values from Appendix 4.

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 90

Trinitrotoluene (TNT) is a highly explosive compound. The thermal decomposition of TNT is described by the following chemical equation: $$2 \mathrm{C}_{7} \mathrm{H}_{5} \mathrm{N}_{3} \mathrm{O}_{6}(s) \rightarrow 12 \mathrm{CO}(g)+5 \mathrm{H}_{2}(g)+3 \mathrm{N}_{2}(g)+2 \mathrm{C}(s)$$ If $\Delta H_{\text {rxn }}^{\circ}$ for the reaction is $-10,153 \mathrm{kJ} / \mathrm{mol}$, how much TNT is needed to equal the explosive power of one mole of ammonium nitrate (see Problem $9.89) ?$

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 91

Fertilizer (ammonium nitrate) and fuel oil (a mixture of long-chain hydrocarbons similar to decane, $\left.\mathrm{C}_{10} \mathrm{H}_{22}\right)$ can form an explosive mixture. Determine the enthalpy change of the following explosive reaction using the appropriate enthalpies of formation (the standard enthalpy of formation of liquid $\mathrm{C}_{10} \mathrm{H}_{22}$ is $249.7 \mathrm{kJ} / \mathrm{mol}$ ). $$\begin{array}{rl} 3 \mathrm{NH}_{4} \mathrm{NO}_{3}(s)+\mathrm{C}_{10} \mathrm{H}_{22}(\ell)+ & 14 \mathrm{O}_{2}(g) \rightarrow \\ 3 & \mathrm{N}_{2}(g)+17 \mathrm{H}_{2} \mathrm{O}(g)+10 \mathrm{CO}_{2}(g) \end{array}$$

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 92

Explosives called amatols are mixtures of ammonium nitrate and trinitrotoluene (TNT) introduced during World War I when TNT was in short supply. The mixtures can provide $30 \%$ more explosive power than TNT alone. Above $300^{\circ} \mathrm{C},$ ammonium nitrate decomposes to $\mathrm{N}_{2}, \mathrm{O}_{2},$ and $\mathrm{H}_{2} \mathrm{O} .$ Write a balanced chemical reaction describing the decomposition of ammonium nitrate, and calculate its $\Delta H_{\mathrm{rxn}}^{\circ}$ using the appropriate $\Delta H_{\mathrm{f}}^{\circ}$ values from Appendix 4.

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 93

Use the average bond energy values in Table A4.1 of Appendix 4 to answer.
Use average bond energies to estimate the enthalpy changes of the following reactions under standard conditions:
a. $\mathrm{N}_{2}(g)+3 \mathrm{H}_{2}(g) \rightarrow 2 \mathrm{NH}_{3}(g)$
b. $\mathrm{N}_{2}(g)+2 \mathrm{H}_{2}(g) \rightarrow \mathrm{H}_{2} \mathrm{NNH}_{2}(g)$
c. $2 \mathrm{N}_{2}(g)+\mathrm{O}_{2}(g) \rightarrow 2 \mathrm{N}_{2} \mathrm{O}(g)$

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 94

Use the average bond energy values in Table A4.1 of Appendix 4 to answer.
Use average bond energies to estimate the enthalpy changes of the following reactions under standard conditions:
a. $\mathrm{CO}_{2}(g)+\mathrm{H}_{2}(g) \rightarrow \mathrm{H}_{2} \mathrm{O}(g)+\mathrm{CO}(g)$
b. $\mathrm{N}_{2}(g)+\mathrm{O}_{2}(g) \rightarrow 2 \mathrm{NO}(g)$
c. $\overrightarrow{\mathrm{C}}(s)+\mathrm{CO}_{2}(g) \rightarrow 2 \mathrm{CO}(g)$
Hint: The heat of sublimation of graphite, $\mathrm{C}(s),$ is $719 \mathrm{kJ} / \mathrm{mol} .$

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 95

Use average bond energies to estimate the difference in $\Delta H_{\mathrm{rxn}}^{\circ}$ values between the incomplete combustion of one mole of ethane to carbon monoxide and water vapor and the complete combustion of ethane to carbon dioxide and water vapor.

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 96

Use average bond energies to estimate the difference in $\Delta H_{\mathrm{rxn}}^{\circ}$ values between the reaction $$\mathrm{C}(s)+\mathrm{O}_{2}(g) \rightarrow \mathrm{CO}_{2}(g)$$ and the reaction $$\mathrm{C}(s)+\frac{1}{2} \mathrm{O}_{2}(g) \rightarrow \mathrm{CO}(g)$$

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 97

Use average bond energies to estimate $\Delta H_{\mathrm{rxn}}^{\circ}$ for the following reaction: $$4 \mathrm{NH}_{3}(g)+7 \mathrm{O}_{2}(g) \rightarrow 4 \mathrm{NO}_{2}(g)+6 \mathrm{H}_{2} \mathrm{O}(g)$$

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 98

The value of $\Delta H_{\mathrm{rxn}}^{\circ}$ for the reaction $$2 \mathrm{H}_{2} \mathrm{S}(g)+3 \mathrm{O}_{2}(g) \rightarrow 2 \mathrm{SO}_{2}(g)+2 \mathrm{H}_{2} \mathrm{O}(g)$$ is $-1036 \mathrm{kJ} .$ Estimate the energy of the bonds in $\mathrm{SO}_{2}$.

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 99

How do ion-dipole interactions influence whether an ionic compound's heat of solution is exothermic or endothermic?

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 100

Sodium hydroxide is more soluble in hot water than in cold water, but dissolving sodium hydroxide in water is an exothermic process. How can this be the case?

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 101

What is meant by fuel value?

David Collins

Numerade Educator

Problem 102

What are the units of fuel values?

David Collins

Numerade Educator

Problem 103

Without doing any calculations, predict which compound in each pair releases more energy during combustion:
a. 1 mole of $\mathrm{CH}_{4}$ or 1 mole of $\mathrm{H}_{2}$
b. $1 \mathrm{g}$ of $\mathrm{CH}_{4}$ or $1 \mathrm{g}$ of $\mathrm{H}_{2}$

Lottie Adams

Numerade Educator

Problem 104

Is fuel value or fuel density a more useful measure of energy content of liquid fuels? Explain your answer.

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 105

Use a Born-Haber cycle to calculate the lattice energy of potassium chloride (KCl) from the following data:
$$\begin{aligned}
&\text { Ionization energy of } \mathrm{K}(g)=419 \mathrm{kJ} / \mathrm{mol}\\
&\text { Electron affinity of } \mathrm{Cl}(g)=-349 \mathrm{kJ} / \mathrm{mol}\\
&\text { Energy to sublime } \mathrm{K}(s)=89 \mathrm{kJ} / \mathrm{mol}\\
&\text { Bond energy of } \mathrm{Cl}_{2}(g)=243 \mathrm{kJ} / \mathrm{mol}
\end{aligned}$$
Standard heat of formation of $\mathrm{KCl}=-436.5 \mathrm{kJ} / \mathrm{mol}$

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 106

Calculate the lattice energy of sodium oxide $\left(\mathrm{Na}_{2} \mathrm{O}\right)$ from the following data: Ionization energy of $\mathrm{Na}(g)=495 \mathrm{kJ} / \mathrm{mol}$ Electron affinity of $\mathrm{O}(g)$ for 2 electrons $=603 \mathrm{kJ} / \mathrm{mol}$ Energy to sublime $\mathrm{Na}(s)=109 \mathrm{kJ} / \mathrm{mol}$ Bond energy of $\mathrm{O}_{2}(g)=498 \mathrm{kJ} / \mathrm{mol}$ $\Delta H_{\mathrm{rxn}}$ for $2 \mathrm{Na}(s)+\frac{1}{2} \mathrm{O}_{2}(g) \rightarrow \mathrm{Na}_{2} \mathrm{O}(s)=-416 \mathrm{kJ} / \mathrm{mol}$

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 107

If all the energy obtained from burning 1.00 pound of propane is used to heat water, how many kilograms of water can be heated from $20.0^{\circ} \mathrm{C}$ to $45.0^{\circ} \mathrm{C} ?$

Angelos Evangelinos

Angelos Evangelinos

Numerade Educator

Problem 108

An article in Discover magazine on world-class sprinters contained the following statement: "In one race, a field of eight runners releases enough energy to boil a gallon jug of ice at $0.0^{\circ} \mathrm{C}$ in ten seconds!" How much "energy" do the runners release in 10 seconds? Assume that the ice has a mass of 128 ounces.

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 109

Lightweight camping stoves typically use white gas, a mixture of $\mathrm{C}_{5}$ and $\mathrm{C}_{6}$ hydrocarbons.
a. Calculate the fuel value of $\mathrm{C}_{5} \mathrm{H}_{12},$ given that $\Delta H_{\text {comb }}^{\circ}=$ $-3535 \mathrm{kJ} / \mathrm{mol}$
b. How much heat is released during the combustion of $1.00 \mathrm{kg}$ of $\mathrm{C}_{5} \mathrm{H}_{12} ?$
c. How many grams of $\mathrm{C}_{5} \mathrm{H}_{12}$ must be burned to heat $1.00 \mathrm{kg}$ of water from $20.0^{\circ} \mathrm{C}$ to $90.0^{\circ} \mathrm{C} ?$ Assume that all the heat released during combustion is used to heat the water.

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 110

The heavier (more dense) hydrocarbons in camp stove fuel are hexanes $\left(\mathrm{C}_{6} \mathrm{H}_{14}\right)$.
a. Calculate the fuel value of $\mathrm{C}_{6} \mathrm{H}_{14},$ given that $\Delta H_{\text {comb }}^{\circ}=$ $-4163 \mathrm{kJ} / \mathrm{mol}$.
b. How much heat is released during the combustion of $1.00 \mathrm{kg}$ of $\mathrm{C}_{6} \mathrm{H}_{14} ?$
c. How many grams of $\mathrm{C}_{6} \mathrm{H}_{14}$ are needed to heat $1.00 \mathrm{kg}$ of water from $25.0^{\circ} \mathrm{C}$ to $85.0^{\circ} \mathrm{C} ?$ Assume that all of the heat released during combustion is used to heat the water.
d. Assume white gas is $25 \% \mathrm{C}_{5}$ hydrocarbons (see Problem 9.109) and $75 \%$ C $_{6}$ hydrocarbons; how many grams of white gas are needed to heat $1.00 \mathrm{kg}$ of water from $25.0^{\circ} \mathrm{C}$ to $85.0^{\circ} \mathrm{C} ?$

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 111

The industrial production of hydrogen chloride gas is most frequently carried out by direct synthesis from hydrogen and chlorine: $$\mathrm{H}_{2}(g)+\mathrm{Cl}_{2}(g) \rightarrow 2 \mathrm{HCl}(g)$$ Smaller quantities of HCl $(g)$ may be produced on the laboratory scale by the reaction of sodium chloride and sulfuric acid: $$2 \mathrm{NaCl}(s)+\mathrm{H}_{2} \mathrm{SO}_{4}(\ell) \rightarrow 2 \mathrm{HCl}(g)+\mathrm{Na}_{2} \mathrm{SO}_{4}(s)$$ Apply concepts discussed in this chapter and data from the appendix to determine if either heating or cooling is required when these reactions are carried out.

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 112

A typical double-patty hamburger from a fast-food establishment contains about 563 Calories. (Remember that the dietary "Calorie" is actually a kilocalorie.) Walking at a brisk pace burns about 4.70 Calories per minute. How many minutes would you need to walk to "burn off" the Calories in one double burger?

Angelos Evangelinos

Angelos Evangelinos

Numerade Educator

Problem 113

A 100.0 mL sample of $1.0 \mathrm{MNaOH}$ is mixed with $50.0 \mathrm{mL}$ of $1.0 \mathrm{M} \mathrm{H}_{2} \mathrm{SO}_{4}$ in a large Styrofoam coffee cup; a thermometer is mounted in the lid of the cup to measure the temperature of the contents. The temperature of each solution before mixing is $22.3^{\circ} \mathrm{C} .$ After mixing, their temperature reaches $31.4^{\circ} \mathrm{C} .$ Assume that (1) the density of the mixed solutions is $1.00 \mathrm{g} / \mathrm{mL},(2)$ the specific heat of the mixed solutions is $4.18 \mathrm{J} /\left(\mathrm{g} \cdot^{\circ} \mathrm{C}\right),$ and (3) no heat is lost to the surroundings.
a. Write a balanced chemical equation for the reaction that takes place in the cup.
b. Is any $\mathrm{NaOH}$ or $\mathrm{H}_{2} \mathrm{SO}_{4}$ left in the cup when the reaction is over?
c. Calculate the enthalpy change per mole of $\mathrm{H}_{2} \mathrm{O}$ produced in the reaction.

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 114

With reference to Problem $9.113,$ what if $65.0 \mathrm{mL}$ of $1.0 \mathrm{M}$ $\mathrm{H}_{2} \mathrm{SO}_{4}$ is mixed with $100.0 \mathrm{mL}$ of $1.0 \mathrm{M} \mathrm{NaOH}$ ? Will the increase in temperature be less than, more than, or the same as that measured in Problem $9.113 ?$

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 115

An insulated container holds $50.0 \mathrm{g}$ of water at $25.0^{\circ} \mathrm{C} .$ A $7.25 \mathrm{g}$ sample of copper that had been heated to $100.1^{\circ} \mathrm{C}$ is dropped into the water. What is the final shared temperature of the copper and the water?

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 116

Magnetite $\left(\mathrm{Fe}_{3} \mathrm{O}_{4}\right)$ is magnetic, whereas iron(II) oxide is not.
a. Write and balance the chemical equation for the formation of magnetite from iron(II) oxide and oxygen.
b. Given that $318 \mathrm{kJ}$ of heat is released for each mole of $\mathrm{Fe}_{3} \mathrm{O}_{4}$ formed, what is the enthalpy change of the balanced reaction of formation of $\mathrm{Fe}_{3} \mathrm{O}_{4}$ from iron(II) oxide and oxygen?

Angelos Evangelinos

Angelos Evangelinos

Numerade Educator

Problem 117

Endothermic compounds have positive standard heats of formation. An example is acetylene, $\mathrm{C}_{2} \mathrm{H}_{2}\left(\Delta \mathrm{H}_{\mathrm{f}}^{\circ}=\right.$ $226.7 \mathrm{kJ} / \mathrm{mol}) .$ Combustion of acetylene in pure oxygen produces a flame hot enough to cut and weld steel.
a. What is the standard heat of combustion of acetylene?
b. What is the fuel value of acetylene, assuming the products are $\mathrm{CO}_{2}$ and $\mathrm{H}_{2} \mathrm{O}$ vapor?

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 118

Balance the following chemical equation, name the reactants and products, and calculate the enthalpy change under standard conditions. $$\mathrm{FeO}(s)+\mathrm{O}_{2}(g) \rightarrow \mathrm{Fe}_{2} \mathrm{O}_{3}(s) \quad \Delta H_{\mathrm{rxn}}^{\circ}= ?$$

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 119

Use appropriate bond energies from Table A4.1 of Appendix 4 to predict whether the reaction in which ethylene forms polyethylene plastic is exothermic, endothermic, or involves no change in enthalpy. The reaction can be written: $$n \mathrm{CH}_{2}=\mathrm{CH}_{2} \rightarrow\left[-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\right]_{n}$$ where the structure in the brackets is the repeating unit of polyethylene and the value of $n$ is typically in the thousands.

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 120

Metabolism of Methanol In December 2011 , over 100 people died in West Bengal, India, after drinking bootleg (illegal) liquor spiked with methanol. Methanol is toxic because it is metabolized in a two-step process that produces formic acid (HCOOH):
$$\begin{aligned} &\mathrm{O}_{2}(g)+2 \mathrm{CH}_{3} \mathrm{OH}(a q) \rightarrow 2 \mathrm{HCOOH}(a q)+2 \mathrm{H}_{2} \mathrm{O}(\ell)\\ &&\Delta H_{\mathrm{rxn}}^{\circ}=-1019.5 \mathrm{kJ} \end{aligned}$$
a. Is the reaction endothermic or exothermic?
b. What change in enthalpy accompanies the metabolism of $60.0 \mathrm{g}$ of methanol?
c. In the first step of the process, methanol is converted into formaldehyde $\left(\mathrm{CH}_{2} \mathrm{O}\right),$ which is then converted into formic acid. Would you expect $\Delta H_{\text {rxn }}^{\circ}$ for the metabolism of one mole of methanol to formaldehyde to be larger or smaller than the conversion of one mole of methanol to formic acid?

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 121

In a high-temperature gas-phase reaction, methanol $\left(\mathrm{CH}_{3} \mathrm{OH}\right)$ reacts with $\mathrm{N}_{2}$ to produce $\mathrm{HCN}$ and $\mathrm{NH}_{3}$. The reaction is endothermic, requiring $164 \mathrm{kJ}$ of thermal energy per mole of methanol under standard conditions.
a. Write a balanced chemical equation for this reaction.
b. Is energy a reactant or a product?
c. What is the change in enthalpy under standard conditions if $60.0 \mathrm{g}$ of $\mathrm{CH}_{3} \mathrm{OH}(g)$ reacts with excess $\mathrm{N}_{2}(g),$ forming $\mathrm{HCN}(g),$ and $\mathrm{NH}_{3}(g) ?$

David Collins

Numerade Educator

Problem 122

Calculate $\Delta H_{\mathrm{rxn}}^{\circ}$ for the reaction $$2 \mathrm{Ni}(s)+\frac{1}{4} \mathrm{S}_{8}(s)+3 \mathrm{O}_{2}(g) \rightarrow 2 \mathrm{NiSO}_{3}(s) \quad \Delta H_{\mathrm{rxn}}^{\circ}=?$$ from the following data:
(1) $\mathrm{NiSO}_{3}(s) \rightarrow \mathrm{NiO}(s)+\mathrm{SO}_{2}(g) \quad \Delta H_{\mathrm{rxn}}^{\circ}=156 \mathrm{kJ}$
(2) $\frac{1}{8} S_{8}(s)+O_{2}(g) \rightarrow \operatorname{SO}_{2}(g) \quad \quad \Delta H_{\operatorname{rxn}}^{\circ}=-297 \mathrm{kJ}$
(3) $\mathrm{Ni}(s)+\frac{1}{2} \mathrm{O}_{2}(g) \rightarrow \mathrm{NiO}_{2}(s) \quad \Delta H_{\mathrm{rxn}}^{\circ}=-241 \mathrm{kJ}$

Angelos Evangelinos

Angelos Evangelinos

Numerade Educator

Problem 123

Use the information in thermochemical equations (1) through ( 3 ) to calculate the value of $\Delta H_{\mathrm{rxn}}^{\circ}$ for the reaction in equation (4).
(1) $\mathrm{Pb}(s)+\frac{1}{2} \mathrm{O}_{2}(g) \rightarrow \mathrm{PbO}(s) \quad \quad \Delta H_{\mathrm{rxn}}^{\circ}=-219 \mathrm{kJ}$
(2) $\mathrm{C}(s)+\mathrm{O}_{2}(g) \rightarrow \mathrm{CO}_{2}(g) \Delta H_{\text {rxn }}^{\circ}=-394 \mathrm{kJ}$
(3) $\mathrm{PbCO}_{3}(s) \rightarrow \mathrm{PbO}(s)+\mathrm{CO}_{2}(g) \quad \Delta H_{\text {rxn }}^{\circ}=86 \mathrm{kJ}$
(4) $2 \mathrm{Pb}(s)+2 \mathrm{C}(s)+3 \mathrm{O}_{2}(g) \rightarrow 2 \mathrm{PbCO}_{3}(s) \quad \Delta H_{\mathrm{rxn}}^{\circ}=?$

Angelos Evangelinos

Angelos Evangelinos

Numerade Educator

Problem 124

Most of the new cars sold in Brazil are flex-fuel vehicles, which means they can run on blends of ethanol and gasoline or on pure ethanol alone. Ethanol is a popular liquid fuel in Brazil because it can be efficiently produced by fermenting sugar extracted from sugarcane. Use appropriate standard heats of formation to calculate the enthalpy change that accompanies the combustion of one mole of liquid ethanol in which the products are $\mathrm{CO}_{2}$ and $\mathrm{H}_{2} \mathrm{O}$ vapor.

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 125

Baking soda (NaHCO $_{3}$ ) thermally decomposes to soda ash $\left(\mathrm{Na}_{2} \mathrm{CO}_{3}\right), \mathrm{CO}_{2},$ and $\mathrm{H}_{2} \mathrm{O}:$ $$2 \mathrm{NaHCO}_{3}(s) \rightarrow \mathrm{Na}_{2} \mathrm{CO}_{3}(s)+\mathrm{CO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(g)$$ Use appropriate standard heats of formation to calculate the enthalpy change that accompanies the thermal decomposition of one mole of $\mathrm{NaHCO}_{3}$.

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 126

In $1819,$ Pierre Dulong and Alexis Petit reported that the product of the atomic mass of a metal times its specific heat is approximately constant, an observation called the law of Dulong and Petit.
a. Explain how the specific heat and molar heat capacity data for the metals in Table 9.3 support this law.
b. Use these data to predict the specific heat values of nickel and platinum.

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 127

Urine odor gets worse with time because it contains the metabolic product urea, $\mathrm{CO}\left(\mathrm{NH}_{2}\right)_{2}, \mathrm{a}$ compound that is slowly converted to carbon dioxide and ammonia, which has a sharp, unpleasant odor: $$\mathrm{CO}\left(\mathrm{NH}_{2}\right)_{2}(a q)+\mathrm{H}_{2} \mathrm{O}(\ell) \rightarrow \mathrm{CO}_{2}(a q)+2 \mathrm{NH}_{3}(a q)$$ This reaction is much too slow for $\Delta H_{\mathrm{rxn}}^{\circ}$ to be determined experimentally by measuring a change in temperature, but it can be calculated from the appropriate $\Delta H_{f}^{\circ}$ values. Calculate $\Delta H_{\mathrm{rxn}}^{\circ} .$ [The value of $\Delta H_{\mathrm{f}}^{\circ}$ of $\mathrm{CO}\left(\mathrm{NH}_{2}\right)_{2}(a q)$ is $-319.2 \mathrm{kJ} / \mathrm{mol} .]$

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 128

Propane is a gas at 1 bar of pressure above $-42^{\circ} \mathrm{C},$ though it is transported as a liquid under pressure. How does the physical state of propane affect its fuel value and its fuel density?

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 129

The payload of a rocket includes a fuel and oxygen for combustion of the fuel. Reactions ( 1 ) and (2) describe the combustion of dimethylhydrazine and hydrogen, respectively. Pound for pound, which is the better rocket fuel?
(1) $\left(\mathrm{CH}_{3}\right)_{2} \mathrm{NNH}_{2}(\ell)+4 \mathrm{O}_{2}(g) \rightarrow$ $\mathrm{N}_{2}(g)+4 \mathrm{H}_{2} \mathrm{O}(g)+2 \mathrm{CO}_{2}(g) \quad \Delta H_{\mathrm{ran}}^{\circ}=-1694 \mathrm{kJ}$
(2) $\mathrm{H}_{2}(g)+\frac{1}{2} \mathrm{O}_{2}(g) \rightarrow \mathrm{H}_{2} \mathrm{O}(g) \quad \quad \Delta H_{\mathrm{rxn}}^{\circ}=-241.8 \mathrm{kJ}$

Ronald Prasad

Numerade Educator

Problem 130

At high temperatures, such as those in the combustion chambers of automobile engines, nitrogen and oxygen form nitrogen monoxide: $$\mathrm{N}_{2}(g)+\mathrm{O}_{2}(g) \rightarrow 2 \mathrm{NO}(g) \quad \Delta H_{\mathrm{comb}}^{\circ}=+180 \mathrm{kJ}$$ Any NO released into the environment may be oxidized to $\mathrm{NO}_{2}:$ $$2 \mathrm{NO}(g)+\mathrm{O}_{2}(g) \rightarrow 2 \mathrm{NO}_{2}(g) \quad \Delta H_{\mathrm{comb}}^{\circ}=-112 \mathrm{kJ}$$ Is the overall reaction, $$\mathrm{N}_{2}(g)+2 \mathrm{O}_{2}(g) \rightarrow 2 \mathrm{NO}_{2}(g)$$ exothermic or endothermic? What is $\Delta H_{\text {comb }}^{\circ}$ for this reaction?

David Collins

Numerade Educator