Chemistry

Raymond Chang, Jason Overby

Chapter 6

Thermochemistry - all with Video Answers

Educators

+ 2 more educators

Chapter Questions

Problem 1

Define these terms: system, surroundings, open system, closed system, isolated system, thermal energy, chemical energy, potential energy, kinetic energy, law of conservation of energy.

Nicole Bylsma

Nicole Bylsma

Numerade Educator

Problem 2

What is heat? How does heat differ from thermal energy? Under what condition is heat transferred from one system to another?

Daniel Kim

Numerade Educator

Problem 3

What are the units for energy commonly employed in chemistry?

Nicole Bylsma

Numerade Educator

Problem 4

A truck initially traveling at $60 \mathrm{~km}$ per hour is brought to a complete stop at a traffic light. Does this change violate the law of conservation of energy? Explain.

Daniel Kim

Numerade Educator

Problem 5

These are various forms of energy: chemical, heat, light, mechanical, and electrical. Suggest ways of interconverting these forms of energy.

Nicole Bylsma

Numerade Educator

Problem 6

Describe the interconversions of forms of energy occurring in these processes: (a) You throw a softball up into the air and catch it. (b) You switch on a flashlight. (c) You ride the ski lift to the top of the hill and then ski down. (d) You strike a match and let it burn down.

Daniel Kim

Numerade Educator

Problem 7

Define these terms: thermochemistry, exothermic process, endothermic process.

Nicole Bylsma

Numerade Educator

Problem 8

Stoichiometry is based on the law of conservation of mass. On what law is thermochemistry based?

Daniel Kim

Numerade Educator

Problem 9

Describe two exothermic processes and two endothermic processes.

Rachel Vallejo

Numerade Educator

Problem 10

Decomposition reactions are usually endothermic, whereas combination reactions are usually exothermic. Give a qualitative explanation for these trends.

Pam Owens

Numerade Educator

Problem 11

On what law is the first law of thermodynamics based? Explain the sign conventions in the equation $\Delta U=q+w$

Nicole Bylsma

Numerade Educator

Problem 12

Explain what is meant by a state function. Give two examples of quantities that are state functions and two that are not.

Daniel Kim

Numerade Educator

Problem 13

The internal energy of an ideal gas depends only on its temperature. Do a first-law analysis of this process. A sample of an ideal gas is allowed to expand at constant temperature against atmospheric pressure. (a) Does the gas do work on its surroundings? (b) Is there heat exchange between the system and the surroundings? If so, in which direction?
(c) What is $\Delta U$ for the gas for this process?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 14

Consider these changes:
(a) $\mathrm{Hg}(l) \longrightarrow \mathrm{Hg}(g)$
(b) $3 \mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{O}_{3}(g)$
(c) $\mathrm{CuSO}_{4} \cdot 5 \mathrm{H}_{2} \mathrm{O}(s) \longrightarrow \mathrm{CuSO}_{4}(s)+5 \mathrm{H}_{2} \mathrm{O}(g)$
(d) $\mathrm{H}_{2}(g)+\mathrm{F}_{2}(g) \longrightarrow 2 \mathrm{HF}(g)$
At constant pressure, in which of the reactions is work done by the system on the surroundings? By the surroundings on the system? In which of them is no work done?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 15

A sample of nitrogen gas expands in volume from $1.6 \mathrm{~L}$ to $5.4 \mathrm{~L}$ at constant temperature. Calculate the work done in joules if the gas expands (a) against a vacuum, (b) against a constant pressure of 0.80 atm, and (c) against a constant pressure of 3.7 atm.

Nicole Bylsma

Numerade Educator

Problem 16

A gas expands in volume from $26.7 \mathrm{~mL}$ to $89.3 \mathrm{~mL}$ at constant temperature. Calculate the work done (in joules) if the gas expands (a) against a vacuum,
(b) against a constant pressure of 1.5 atm, and
(c) against a constant pressure of 2.8 atm.

Daniel Kim

Numerade Educator

Problem 17

A gas expands and does $P-V$ work on the surroundings equal to $325 \mathrm{~J}$. At the same time, it absorbs $127 \mathrm{~J}$ of heat from the surroundings. Calculate the change in energy of the gas.

Rachel Vallejo

Numerade Educator

Problem 18

The work done to compress a gas is $74 \mathrm{~J}$. As a result, $26 \mathrm{~J}$ of heat is given off to the surroundings. Calculate the change in energy of the gas.

Daniel Kim

Numerade Educator

Problem 19

Calculate the work done when $50.0 \mathrm{~g}$ of tin dissolves in excess acid at 1.00 atm and $25^{\circ} \mathrm{C}$ :
$$\operatorname{sn}(s)+2 \mathrm{H}^{+}(a q) \longrightarrow \operatorname{Sn}^{2+}(a q)+\mathrm{H}_{2}(g)$$
Assume ideal gas behavior.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 20

Calculate the work done in joules when 1.0 mole of water vaporizes at 1.0 atm and $100^{\circ} \mathrm{C}$. Assume that the volume of liquid water is negligible compared with that of steam at $100^{\circ} \mathrm{C}$, and ideal gas behavior.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 21

Define these terms: enthalpy, enthalpy of reaction. Under what condition is the heat of a reaction equal to the enthalpy change of the same reaction?

Rachel Vallejo

Numerade Educator

Problem 22

In writing thermochemical equations, why is it important to indicate the physical state (that is, gaseous, liquid, solid, or aqueous) of each substance?

Daniel Kim

Numerade Educator

Problem 23

Explain the meaning of this thermochemical equation:
$$\begin{array}{r}4 \mathrm{NH}_{3}(g)+5 \mathrm{O}_{2}(g) \longrightarrow 4 \mathrm{NO}(g)+6 \mathrm{H}_{2} \mathrm{O}(g) \\\Delta H=-904 \mathrm{~kJ} / \mathrm{mol}\end{array}$$

Rachel Vallejo

Numerade Educator

Problem 24

Consider this reaction:
$$\begin{array}{r}2 \mathrm{CH}_{3} \mathrm{OH}(l)+3 \mathrm{O}_{2}(g) \longrightarrow 4 \mathrm{H}_{2} \mathrm{O}(l)+2 \mathrm{CO}_{2}(g) \\\Delta H=-1452.8 \mathrm{~kJ} / \mathrm{mol}\end{array}$$
What is the value of $\Delta H$ if (a) the equation is multiplied throughout by $2,$ (b) the direction of the reaction is reversed so that the products become the reactants and vice versa, (c) water vapor instead of liquid water is formed as the product?

Daniel Kim

Numerade Educator

Problem 25

The first step in the industrial recovery of zinc from the zinc sulfide ore is roasting, that is, the conversion of $\mathrm{ZnS}$ to $\mathrm{ZnO}$ by heating:
$$\begin{array}{r}2 \mathrm{ZnS}(s)+3 \mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{ZnO}(s)+2 \mathrm{SO}_{2}(g) \\
\Delta H=-879 \mathrm{~kJ} / \mathrm{mol}\end{array}$$
Calculate the heat evolved (in kJ) per gram of ZnS roasted.

Nicole Bylsma

Numerade Educator

Problem 26

Determine the amount of heat (in kJ) given off when $1.26 \times 10^{4} \mathrm{~g}$ of $\mathrm{NO}_{2}$ are produced according to the equation
$$\begin{array}{r}2 \mathrm{NO}(g)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{NO}_{2}(g) \\\Delta H=-114.6 \mathrm{~kJ} / \mathrm{mol}\end{array}$$

Daniel Kim

Numerade Educator

Problem 27

Consider the reaction
$$\begin{array}{r}2 \mathrm{H}_{2} \mathrm{O}(g) \longrightarrow 2 \mathrm{H}_{2}(g)+\mathrm{O}_{2}(g) \\
\Delta H=483.6 \mathrm{~kJ} / \mathrm{mol}\end{array}$$
If 2.0 moles of $\mathrm{H}_{2} \mathrm{O}(g)$ are converted to $\mathrm{H}_{2}(g)$ and $\mathrm{O}_{2}(g)$ against a pressure of $1.0 \mathrm{~atm}$ at $125^{\circ} \mathrm{C},$ what is $\Delta U$ for this reaction?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 28

Consider the reaction
$$\begin{array}{r}\mathrm{H}_{2}(g)+\mathrm{Cl}_{2}(g) \longrightarrow 2 \mathrm{HCl}(g) \\
\Delta H=-184.6 \mathrm{~kJ} / \mathrm{mol}\end{array}$$
If 3 moles of $\mathrm{H}_{2}$ react with 3 moles of $\mathrm{Cl}_{2}$ to form $\mathrm{HCl},$ calculate the work done (in joules) against a pressure of 1.0 atm at $25^{\circ} \mathrm{C}$. What is $\Delta U$ for this reaction? Assume the reaction goes to completion.

Noah Boudrie

Numerade Educator

Problem 29

What is the difference between specific heat and heat capacity? What are the units for these two quantities? Which is the intensive property and which is the extensive property?

Nicole Bylsma

Numerade Educator

Problem 30

Define calorimetry and describe two commonly used calorimeters. In a calorimetric measurement, why is it important that we know the heat capacity of the calorimeter? How is this value determined?

Daniel Kim

Numerade Educator

Problem 31

Consider the following data: $$
\begin{array}{lcc}
\text { Metal } & \text { Al } & \text { Cu } \\
\hline \text { Mass (g) } & 10 & 30 \\
\text { Specific heat (J/g* } \left.^{\circ} \mathrm{C}\right) & 0.900 & 0.385 \\
\text { Temperature }\left({ }^{\circ} \mathrm{C}\right) & 40 & 60 \\
\hline
\end{array}
$$ When these two metals are placed in contact, which of the following will take place? (a) Heat will flow from Al to Cu because Al has a larger specific heat.
(b) Heat will flow from $\mathrm{Cu}$ to $\mathrm{Al}$ because $\mathrm{Cu}$ has a larger mass.
(c) Heat will flow from Cu to Al because Cu has a larger heat capacity.
(d) Heat will flow from Cu to Al because Cu is at a higher temperature.
(e) No heat will flow in either direction.

Nicole Bylsma

Numerade Educator

Problem 32

A piece of silver of mass $362 \mathrm{~g}$ has a heat capacity of $85.7 \mathrm{~J} /{ }^{\circ} \mathrm{C}$. What is the specific heat of silver?

Daniel Kim

Numerade Educator

Problem 33

A 6.22 -kg piece of copper metal is heated from $20.5^{\circ} \mathrm{C}$ to $324.3^{\circ} \mathrm{C} .$ Calculate the heat absorbed (in kJ) by the metal.

Chareen Guzman

Numerade Educator

Problem 34

Calculate the amount of heat liberated (in kJ) from $366 \mathrm{~g}$ of mercury when it cools from $77.0^{\circ} \mathrm{C}$ to $12.0^{\circ} \mathrm{C}$

Daniel Kim

Numerade Educator

Problem 35

A sheet of gold weighing $10.0 \mathrm{~g}$ and at a temperature of $18.0^{\circ} \mathrm{C}$ is placed flat on a sheet of iron weighing $20.0 \mathrm{~g}$ and at a temperature of $55.6^{\circ} \mathrm{C}$. What is the final temperature of the combined metals? Assume that no heat is lost to the surroundings. (Hint: The heat gained by the gold must be equal to the heat lost by the iron. The specific heats of the metals are given in Table $6.2 . ?$

Nicole Bylsma

Numerade Educator

Problem 36

To a sample of water at $23.4^{\circ} \mathrm{C}$ in a constantpressure calorimeter of negligible heat capacity is added a $12.1-\mathrm{g}$ piece of aluminum whose temperature is $81.7^{\circ} \mathrm{C}$. If the final temperature of water is $24.9^{\circ} \mathrm{C},$ calculate the mass of the water in the calorimeter.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 37

A 0.1375-g sample of solid magnesium is burned in a constant-volume bomb calorimeter that has a heat capacity of $3024 \mathrm{~J} /{ }^{\circ} \mathrm{C}$. The temperature increases by $1.126^{\circ} \mathrm{C} .$ Calculate the heat given off by the burning $\mathrm{Mg},$ in $\mathrm{kJ} / \mathrm{g}$ and in $\mathrm{kJ} / \mathrm{mol} .$

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 38

A quantity of $85.0 \mathrm{~mL}$ of $0.900 \mathrm{M} \mathrm{HCl}$ is mixed with $85.0 \mathrm{~mL}$ of $0.900 \mathrm{M}$ KOH in a constantpressure calorimeter that has a heat capacity of $325 \mathrm{~J} /{ }^{\circ} \mathrm{C}$. If the initial temperatures of both solutions are the same at $18.24^{\circ} \mathrm{C},$ what is the final temperature of the mixed solution? The heat of neutralization is $-56.2 \mathrm{~kJ} / \mathrm{mol} .$ Assume the density and specific heat of the solutions are the same as those for water.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 39

What is meant by the standard-state condition?

Rachel Vallejo

Numerade Educator

Problem 40

How are the standard enthalpies of an element and a compound determined?

Daniel Kim

Numerade Educator

Problem 41

What is meant by the standard enthalpy of a reaction?

Rachel Vallejo

Numerade Educator

Problem 42

Write the equation for calculating the enthalpy of a reaction. Define all the terms.

Daniel Kim

Numerade Educator

Problem 43

State Hess's law. Explain, with one example, the usefulness of this law in thermochemistry.

Rachel Vallejo

Numerade Educator

Problem 44

Describe how chemists use Hess's law to determine the $\Delta H_{\mathrm{f}}^{\circ}$ of a compound by measuring its heat (enthalpy of combustion.

Rachel Vallejo

Numerade Educator

Problem 45

Which of the following standard enthalpy of formation values is not zero at $25^{\circ} \mathrm{C} ? \mathrm{Na}(s), \operatorname{Ne}(g)$
$\mathrm{CH}_{4}(g), \mathrm{S}_{8}(s), \mathrm{Hg}(l), \mathrm{H}(g)$

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 46

The $\Delta H_{\mathrm{f}}^{\circ}$ values of the two allotropes of oxygen, $\mathrm{O}_{2}$ and $\mathrm{O}_{3}$, are 0 and $142.2 \mathrm{~kJ} / \mathrm{mol}$, respectively, at $25^{\circ} \mathrm{C}$. Which is the more stable form at this temperature?

Daniel Kim

Numerade Educator

Problem 47

Which is the more negative quantity at $25^{\circ} \mathrm{C}: \Delta H_{\mathrm{f}}^{\circ}$ for $\mathrm{H}_{2} \mathrm{O}(l)$ or $\Delta H_{\mathrm{f}}^{\circ}$ for $\mathrm{H}_{2} \mathrm{O}(g) ?$

Rachel Vallejo

Numerade Educator

Problem 48

Predict the value of $\Delta H_{\mathrm{f}}^{\circ}$ (greater than, less than, or equal to zero) for these elements at $25^{\circ} \mathrm{C}:$ (a) $\mathrm{Br}_{2}(g)$ $\mathrm{Br}_{2}(l)$
(b) $\mathrm{I}_{2}(g) ; \mathrm{I}_{2}(s)$

Daniel Kim

Numerade Educator

Problem 49

In general, compounds with negative $\Delta H_{i}^{\circ}$ values are more stable than those with positive $\Delta H_{i}^{\circ}$ values. $\mathrm{H}_{2} \mathrm{O}_{2}(l)$ has a negative $\Delta H_{\mathrm{f}}^{\circ}$ (see Table 6.4 ). Why, then, does $\mathrm{H}_{2} \mathrm{O}_{2}(l)$ have a tendency to decompose to $\mathrm{H}_{2} \mathrm{O}(l)$ and $\mathrm{O}_{2}(g) ?$

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 50

Suggest ways (with appropriate equations) that would enable you to measure the $\Delta H_{\mathrm{f}}^{\circ}$ values of $\mathrm{Ag}_{2} \mathrm{O}(s)$ and $\mathrm{CaCl}_{2}(s)$ from their elements. No calculations are necessary.

Daniel Kim

Numerade Educator

Problem 51

Calculate the heat of decomposition for this process at constant pressure and $25^{\circ} \mathrm{C}$ :
$$\mathrm{CaCO}_{3}(s) \longrightarrow \mathrm{CaO}(s)+\mathrm{CO}_{2}(g)$$
(Look up the standard enthalpy of formation of the reactant and products in Table $6.4 .)$

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 52

The standard enthalpies of formation of ions in aqueous solutions are obtained by arbitrarily assigning a value of zero to $\mathrm{H}^{+}$ ions; that is, $\Delta H_{\mathrm{f}}^{\circ}\left[\mathrm{H}^{+}(a q)\right]=0$
(a) For the following reaction
$$\begin{array}{r}\mathrm{HCl}(g) \stackrel{\mathrm{H}_{2} \mathrm{O}}{\longrightarrow} \mathrm{H}^{+}(aq)+\mathrm{Cl}^{-}(a q) \\\Delta H^{\circ}=-74.9 \mathrm{~kJ} / \mathrm{mol}\end{array}$$
calculate $\Delta H_{\mathrm{f}}^{\circ}$ for the $\mathrm{Cl}^{-}$ ions.
(b) Given that $\Delta H_{\mathrm{f}}^{\circ}$ for $\mathrm{OH}^{-}$ ions is $-229.6 \mathrm{~kJ} / \mathrm{mol}$, calculate the enthalpy of neutralization when 1 mole of a strong monoprotic acid (such as $\mathrm{HCl}$ ) is titrated by 1 mole of a strong base (such as $\mathrm{KOH}$ ) at $25^{\circ} \mathrm{C}$.

Rachel Vallejo

Numerade Educator

Problem 53

Calculate the heats of combustion for the following reactions from the standard enthalpies of formation listed in Appendix 2 :
(a) $2 \mathrm{H}_{2}(g)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{H}_{2} \mathrm{O}(l)$
(b) $2 \mathrm{C}_{2} \mathrm{H}_{2}(g)+5 \mathrm{O}_{2}(g) \longrightarrow 4 \mathrm{CO}_{2}(g)+2 \mathrm{H}_{2} \mathrm{O}(l)$

Rachel Vallejo

Numerade Educator

Problem 54

Calculate the heats of combustion for the following reactions from the standard enthalpies of formation listed in Appendix 2 :
(a) $\mathrm{C}_{2} \mathrm{H}_{4}(g)+3 \mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{CO}_{2}(g)+2 \mathrm{H}_{2} \mathrm{O}(l)$
(b) $2 \mathrm{H}_{2} \mathrm{~S}(g)+3 \mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{H}_{2} \mathrm{O}(l)+2 \mathrm{SO}_{2}(g)$

Rachel Vallejo

Numerade Educator

Problem 55

Methanol, ethanol, and $n$ -propanol are three common alcohols. When $1.00 \mathrm{~g}$ of each of these alcohols is burned in air, heat is liberated as shown by the following data:
(a) methanol $\left(\mathrm{CH}_{3} \mathrm{OH}\right)$ $-22.6 \mathrm{~kJ} ;(\mathrm{b})$ ethanol $\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\right),-29.7 \mathrm{~kJ} ;$
(c) $n$ -propanol $\left(\mathrm{C}_{3} \mathrm{H}_{7} \mathrm{OH}\right),-33.4 \mathrm{~kJ} .$ Calculate the heats of combustion of these alcohols in $\mathrm{kJ} / \mathrm{mol}$.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 56

The standard enthalpy change for the following reaction is $436.4 \mathrm{~kJ} / \mathrm{mol}:$
$$\mathrm{H}_{2}(g) \longrightarrow \mathrm{H}(g)+\mathrm{H}(g)$$
Calculate the standard enthalpy of formation of atomic hydrogen (H).

Daniel Kim

Numerade Educator

Problem 57

From the standard enthalpies of formation, calculate $\Delta H_{\mathrm{rxn}}^{\circ}$ for the reaction
$$\mathrm{C}_{6} \mathrm{H}_{12}(l)+9 \mathrm{O}_{2}(g) \longrightarrow 6 \mathrm{CO}_{2}(g)+6 \mathrm{H}_{2} \mathrm{O}(l)$$
For $\mathrm{C}_{6} \mathrm{H}_{12}(l), \Delta H_{\mathrm{f}}^{\circ}=-151.9 \mathrm{~kJ} / \mathrm{mol}$

Rachel Vallejo

Numerade Educator

Problem 58

Pentaborane-9, $\mathrm{B}_{5} \mathrm{H}_{9}$, is a colorless, highly reactive liquid that will burst into flame when exposed to oxygen. The reaction is
$$2 \mathrm{~B}_{5} \mathrm{H}_{9}(l)+12 \mathrm{O}_{2}(g) \longrightarrow 5 \mathrm{~B}_{2} \mathrm{O}_{3}(s)+9 \mathrm{H}_{2} \mathrm{O}(l)$$
Calculate the kilojoules of heat released per gram of the compound reacted with oxygen. The standard enthalpy of formation of $\mathrm{B}_{5} \mathrm{H}_{9}$ is $73.2 \mathrm{~kJ} / \mathrm{mol} .$

Daniel Kim

Numerade Educator

Problem 59

Determine the amount of heat (in kJ) given off when $1.26 \times 10^{4} \mathrm{~g}$ of ammonia are produced according to the equation
$$\begin{aligned}\mathrm{N}_{2}(g)+3 \mathrm{H}_{2}(g) \longrightarrow & 2 \mathrm{NH}_{3}(g) \\
& \Delta H_{\mathrm{rxn}}^{\circ}=-92.6 \mathrm{~kJ} / \mathrm{mol}
\end{aligned}$$
Assume that the reaction takes place under standardstate conditions at $25^{\circ} \mathrm{C}$.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 60

At $850^{\circ} \mathrm{C}, \mathrm{CaCO}_{3}$ undergoes substantial decomposition to yield $\mathrm{CaO}$ and $\mathrm{CO}_{2}$. Assuming that the $\Delta H_{\mathrm{f}}^{\circ}$ values of the reactant and products are the same at $850^{\circ} \mathrm{C}$ as they are at $25^{\circ} \mathrm{C},$ calculate the enthalpy change (in kJ) if $66.8 \mathrm{~g}$ of $\mathrm{CO}_{2}$ are produced in one reaction.

Daniel Kim

Numerade Educator

Problem 61

From the following data,
$$
\begin{array}{c}
\mathrm{C} \text { (graphite) }+\mathrm{O}_{2}(g) \longrightarrow \mathrm{CO}_{2}(g) \\
\Delta H_{\mathrm{rxn}}^{\circ}=-393.5 \mathrm{~kJ} / \mathrm{mol} \\
\mathrm{H}_{2}(g)+\frac{1}{2} \mathrm{O}_{2}(g) \longrightarrow \mathrm{H}_{2} \mathrm{O}(l) \\
\Delta H_{\mathrm{rxn}}^{\circ}=-285.8 \mathrm{~kJ} / \mathrm{mol} \\
2 \mathrm{C}_{2} \mathrm{H}_{6}(g)+7 \mathrm{O}_{2}(g) \longrightarrow 4 \mathrm{CO}_{2}(g)+6 \mathrm{H}_{2} \mathrm{O}(l) \\
\Delta H_{\mathrm{rxn}}^{\circ}=-3119.6 \mathrm{~kJ} / \mathrm{mol}
\end{array}
$$
calculate the enthalpy change for the reaction
$$
2 \mathrm{C}(\text { graphite })+3 \mathrm{H}_{2}(g) \longrightarrow \mathrm{C}_{2} \mathrm{H}_{6}(g)
$$

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 62

From the following data,
$$\begin{array}{r}\mathrm{C}(\text { graphite })+\mathrm{O}_{2}(g) \longrightarrow \mathrm{CO}_{2}(g) \\
\Delta H_{\mathrm{rxn}}^{\circ}=-393.5 \mathrm{~kJ} / \mathrm{mol} \\
\mathrm{H}_{2}(g)+\frac{1}{2} \mathrm{O}_{2}(g) \longrightarrow \mathrm{H}_{2} \mathrm{O}(l) \\
\Delta H_{\mathrm{rxn}}^{\circ}=-285.8 \mathrm{~kJ} / \mathrm{mol} \\2 \mathrm{C}_{2} \mathrm{H}_{6}(g)+7 \mathrm{O}_{2}(g) \longrightarrow 4 \mathrm{CO}_{2}(g)+6 \mathrm{H}_{2} \mathrm{O}(l) \\\Delta H_{\mathrm{rxn}}^{\circ}=-3119.6 \mathrm{~kJ} / \mathrm{mol}
\end{array}
$$calculate the enthalpy change for the reaction$$2 \mathrm{C}(\text { graphite })+3 \mathrm{H}_{2}(g) \longrightarrow \mathrm{C}_{2} \mathrm{H}_{6}(g)$$

Daniel Kim

Numerade Educator

Problem 63

From the following heats of combustion,
$$\begin{array}{r}\mathrm{CH}_{3} \mathrm{OH}(l)+\frac{3}{2} \mathrm{O}_{2}(g) \longrightarrow \mathrm{CO}_{2}(g)+2 \mathrm{H}_{2} \mathrm{O}(l) \\\Delta H_{\mathrm{rxn}}^{\circ}=-726.4 \mathrm{~kJ} / \mathrm{mol} \\\mathrm{C}(\mathrm{graphite})+\mathrm{O}_{2}(g) \longrightarrow \mathrm{CO}_{2}(g) \\
\Delta H_{\mathrm{rxn}}^{\circ}=-393.5 \mathrm{~kJ} / \mathrm{mol} \\
\mathrm{H}_{2}(g)+\frac{1}{2} \mathrm{O}_{2}(g) \longrightarrow \mathrm{H}_{2} \mathrm{O}(l) \\\Delta H_{\mathrm{rxn}}^{\circ}=-285.8 \mathrm{~kJ} / \mathrm{mol}\end{array}$$
calculate the enthalpy of formation of methanol $\left(\mathrm{CH}_{3} \mathrm{OH}\right)$ from its elements:
$$\mathrm{C}(\text { graphite })+2 \mathrm{H}_{2}(g)+\frac{1}{2} \mathrm{O}_{2}(g) \longrightarrow\mathrm{CH}_{3} \mathrm{OH}(l)$$

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 64

Calculate the standard enthalpy change for the reaction
$$2 \mathrm{Al}(s)+\mathrm{Fe}_{2} \mathrm{O}_{3}(s) \longrightarrow 2 \mathrm{Fe}(s)+\mathrm{Al}_{2}\mathrm{O}_{3}(s)$$
given that$$\begin{array}{l}2 \mathrm{Al}(s)+\frac{3}{2} \mathrm{O}_{2}(g) \longrightarrow \mathrm{Al}_{2}\mathrm{O}_{3}(s) \\\Delta H_{\mathrm{rxn}}^{\circ}=-1669.8 \mathrm{~kJ} / \mathrm{mol} \\
2 \mathrm{Fe}(s)+\frac{3}{2} \mathrm{O}_{2}(g) \longrightarrow \mathrm{Fe}_{2} \mathrm{O}_{3}(s) \\\Delta H_{\mathrm{rxn}}^{\circ}=-822.2 \mathrm{~kJ} / \mathrm{mol}\end{array}$$

Nicole Krahulik

Nicole Krahulik

Numerade Educator

Problem 65

Define the following terms: enthalpy of solution, heat of hydration, lattice energy, heat of dilution.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 66

Why is the lattice energy of a solid always a positive quantity? Why is the hydration of ions always a negative quantity?

Ronald Prasad

Numerade Educator

Problem 67

Consider two ionic compounds A and B. A has a larger lattice energy than B. Which of the two compounds is more stable?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 68

$\mathrm{Mg}^{2+}$ is a smaller cation than $\mathrm{Na}^{+}$ and also carries more positive charge. Which of the two species has a larger hydration energy (in $\mathrm{kJ} / \mathrm{mol}$ ) ? Explain.

Anand Jangid

Numerade Educator

Problem 69

Consider the dissolution of an ionic compound such as potassium fluoride in water. Break the process into the following steps: separation of the cations and anions in the vapor phase and the hydration of the ions in the aqueous medium. Discuss the energy changes associated with each step. How does the heat of solution of $\mathrm{KF}$ depend on the relative magnitudes of these two quantities? On what law is the relationship based?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 70

Why is it dangerous to add water to a concentrated acid such as sulfuric acid in a dilution process?

Daniel Kim

Numerade Educator

Problem 71

Which of the following does not have $\Delta H_{\mathrm{f}}^{\circ}=0$ at $25^{\circ} \mathrm{C} ?$
$\begin{array}{lllll}\text { He }(g) & \text { Fe }(s) & \text { Cl }(g) & \text { S }_{8}(s) & \text { O }_{2}(g) & \text { Br }_{2}(l)\end{array}$

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 72

Calculate the expansion work done when 3.70 moles of ethanol are converted to vapor at its boiling point $\left(78.3^{\circ} \mathrm{C}\right)$ and $1.0 \mathrm{~atm}$

Daniel Kim

Numerade Educator

Problem 73

The convention of arbitrarily assigning a zero enthalpy value for the most stable form of each element in the standard state at $25^{\circ} \mathrm{C}$ is a convenient way of dealing with enthalpies of reactions. Explain why this convention cannot be applied to nuclear reactions.

Rachel Vallejo

Numerade Educator

Problem 74

Given the thermochemical equations:
$$\begin{array}{c}\mathrm{Br}_{2}(l)+\mathrm{F}_{2}(g) \longrightarrow 2 \mathrm{BrF}(g) \\
\Delta H^{\circ}=-188 \mathrm{~kJ} / \mathrm{mol} \\
\mathrm{Br}_{2}(l)+3 \mathrm{~F}_{2}(g) \longrightarrow 2 \mathrm{BrF}_{3}(g) \\
\Delta H^{\circ}=-768 \mathrm{~kJ} / \mathrm{mol}\end{array}
$$calculate the $\Delta H_{\mathrm{rxn}}^{\circ}$ for the reaction$$\operatorname{BrF}(g)+\mathrm{F}_{2}(g) \longrightarrow \operatorname{BrF}_{3}(g)$$

Daniel Kim

Numerade Educator

Problem 75

The standard enthalpy change $\Delta H^{\circ}$ for the thermal decomposition of silver nitrate according to the following equation is $+78.67 \mathrm{~kJ}$ :
$$\mathrm{AgNO}_{3}(s) \longrightarrow \mathrm{AgNO}_{2}(s)+\frac{1}{2} \mathrm{O}_{2}(g)$$
The standard enthalpy of formation of $\mathrm{AgNO}_{3}(s)$ is $-123.02 \mathrm{~kJ} / \mathrm{mol} .$ Calculate the standard enthalpy of formation of $\mathrm{AgNO}_{2}(s)$

Rachel Vallejo

Numerade Educator

Problem 76

Hydrazine, $\mathrm{N}_{2} \mathrm{H}_{4},$ decomposes according to the following reaction:
$$3 \mathrm{~N}_{2} \mathrm{H}_{4}(l) \longrightarrow 4 \mathrm{NH}_{3}(g)+\mathrm{N}_{2}(g)$$
(a) Given that the standard enthalpy of formation of hydrazine is $50.42 \mathrm{~kJ} / \mathrm{mol}$, calculate $\Delta H^{\circ}$ for its decomposition. (b) Both hydrazine and ammonia burn in oxygen to produce $\mathrm{H}_{2} \mathrm{O}(l)$ and $\mathrm{N}_{2}(g) .$ Write balanced equations for each of these processes and calculate $\Delta H^{\circ}$ for each of them. On a mass basis (per $\mathrm{kg}$ ) would hydrazine or ammonia be the better fuel?

Daniel Kim

Numerade Educator

Problem 77

A quantity of $2.00 \times 10^{2} \mathrm{~mL}$ of $0.862 \mathrm{MHCl}$ is mixed with an equal volume of $0.431 M \mathrm{Ba}(\mathrm{OH})_{2}$ in a constant-pressure calorimeter of negligible heat capacity. The initial temperature of the $\mathrm{HCl}$ and $\mathrm{Ba}(\mathrm{OH})_{2}$ solutions is the same at $20.48^{\circ} \mathrm{C}$, For the process
$$\mathrm{H}^{+}(a q)+\mathrm{OH}^{-}(a q) \longrightarrow \mathrm{H}_{2} \mathrm{O}(l)$$
the heat of neutralization is $-56.2 \mathrm{~kJ} / \mathrm{mol}$. What is the final temperature of the mixed solution?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 78

A 3.53-g sample of ammonium nitrate $\left(\mathrm{NH}_{4} \mathrm{NO}_{3}\right)$ was added to $80.0 \mathrm{~mL}$ of water in a constantpressure calorimeter of negligible heat capacity. As a result, the temperature of the water decreased from $21.6^{\circ} \mathrm{C}$ to $18.1^{\circ} \mathrm{C}$. Calculate the heat of solution $\left(\Delta H_{\mathrm{soln}}\right)$ of ammonium nitrate.

Daniel Kim

Numerade Educator

Problem 79

Consider the reaction
$$\begin{aligned}\mathrm{N}_{2}(g)+3 \mathrm{H}_{2}(g) & \longrightarrow 2 \mathrm{NH}_{3}(g) \\
\Delta H_{\mathrm{rxn}}^{\circ} &=-92.6 \mathrm{~kJ} / \mathrm{mol}\end{aligned}$$
If 2.0 moles of $\mathrm{N}_{2}$ react with 6.0 moles of $\mathrm{H}_{2}$ to form $\mathrm{NH}_{3},$ calculate the work done (in joules) against a pressure of 1.0 atm at $25^{\circ} \mathrm{C}$. What is $\Delta U$ for this reaction? Assume the reaction goes to completion.

Ronald Prasad

Numerade Educator

Problem 80

Calculate the heat released when $2.00 \mathrm{~L}$ of $\mathrm{Cl}_{2}(g)$ with a density of $1.88 \mathrm{~g} / \mathrm{L}$ react with an excess of sodium metal at $25^{\circ} \mathrm{C}$ and 1 atm to form sodium chloride.

Daniel Kim

Numerade Educator

Problem 81

Photosynthesis produces glucose, $\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6},$ and oxygen from carbon dioxide and water:
$$6 \mathrm{CO}_{2}+6 \mathrm{H}_{2} \mathrm{O} \longrightarrow \mathrm{C}_{6} \mathrm{H}_{12}\mathrm{O}_{6}+6 \mathrm{O}_{2}$$
(a) How would you determine experimentally the $\Delta H_{\mathrm{rxn}}^{\circ}$ value for this reaction? (b) Solar radiation produces about $7.0 \times 10^{14} \mathrm{~kg}$ glucose a year on Earth. What is the corresponding $\Delta H^{\circ}$ change?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 82

A 2.10 -mole sample of crystalline acetic acid, initially at $17.0^{\circ} \mathrm{C},$ is allowed to melt at $17.0^{\circ} \mathrm{C}$ and is then heated to $118.1^{\circ} \mathrm{C}$ (its normal boiling point) at 1.00 atm. The sample is allowed to vaporize at $118.1^{\circ} \mathrm{C}$ and is then rapidly quenched to $17.0^{\circ} \mathrm{C},$ so that it recrystallizes. Calculate $\Delta H^{\circ}$ for the total process as described.

Daniel Kim

Numerade Educator

Problem 83

Calculate the work done in joules by the reaction
$$2 \mathrm{Na}(s)+2 \mathrm{H}_{2} \mathrm{O}(l) \longrightarrow 2 \mathrm{NaOH}(a q)+\mathrm{H}_{2}(g)$$
when $0.34 \mathrm{~g}$ of Na reacts with water to form hydrogen gas at $0^{\circ} \mathrm{C}$ and $1.0 \mathrm{~atm}$.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 84

You are given the following data: $$\begin{aligned}
\mathrm{H}_{2}(g) & \longrightarrow 2 \mathrm{H}(g) & & \Delta H^{\circ}=436.4 \mathrm{~kJ} / \mathrm{mol} \\\mathrm{Br}_{2}(g) & \longrightarrow 2 \mathrm{Br}(g) & & \Delta H^{\circ}=192.5 \mathrm{~kJ} /\mathrm{mol} \\\mathrm{H}_{2}(g)+\mathrm{Br}_{2}(g) & \longrightarrow 2 \mathrm{HBr}(g) & & \Delta H^{\circ}=-72.4 \mathrm{~kJ} / \mathrm{mol}
\end{aligned}
$$Calculate $\Delta H^{\circ}$ for the reaction$$\mathrm{H}(g)+\operatorname{Br}(g) \longrightarrow \operatorname{HBr}(g)$$

Daniel Kim

Numerade Educator

Problem 85

A gaseous mixture consists of 28.4 mole percent of hydrogen and 71.6 mole percent of methane. A 15.6-L gas sample, measured at $19.4^{\circ} \mathrm{C}$ and 2.23 atm, is burned in air. Calculate the heat released.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 86

When $2.740 \mathrm{~g}$ of Ba reacts with $\mathrm{O}_{2}$ at $298 \mathrm{~K}$ and 1 atm to form $\mathrm{BaO}, 11.14 \mathrm{~kJ}$ of heat are released. What is $\Delta H_{i}^{\circ}$ for $\mathrm{BaO} ?$

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 87

Methanol $\left(\mathrm{CH}_{3} \mathrm{OH}\right)$ is an organic solvent and is also used as a fuel in some automobile engines. From the following data, calculate the standard enthalpy of formation of methanol:
$$
\begin{array}{r}
2 \mathrm{CH}_{3} \mathrm{OH}(l)+3 \mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{CO}_{2}(g)+4 \mathrm{H}_{2} \mathrm{O}(l) \\
\Delta H_{\mathrm{xn}}^{\circ}=-1452.8 \mathrm{~kJ} / \mathrm{mol}
\end{array}
$$

Rachel Vallejo

Numerade Educator

Problem 88

A 44.0-g sample of an unknown metal at $99.0^{\circ} \mathrm{C}$ was placed in a constant-pressure calorimeter containing $80.0 \mathrm{~g}$ of water at $24.0^{\circ} \mathrm{C}$. The final temperature of the system was found to be $28.4^{\circ} \mathrm{C}$. Calculate the specific heat of the metal. (The heat capacity of the calorimeter is $\left.12.4 \mathrm{~J} /{ }^{\circ} \mathrm{C} .\right)$

Daniel Kim

Numerade Educator

Problem 89

Using the data in Appendix $2,$ calculate the enthalpy change for the gaseous reaction shown here.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 90

Producer gas (carbon monoxide) is prepared by passing air over red-hot coke:
$$
\mathrm{C}(s)+\frac{1}{2} \mathrm{O}_{2}(g) \longrightarrow \mathrm{CO}(g)
$$
Water gas (mixture of carbon monoxide and hydrogen) is prepared by passing steam over red-hot coke:
$$\mathrm{C}(s)+\mathrm{H}_{2} \mathrm{O}(g) \longrightarrow \mathrm{CO}(g)+\mathrm{H}_{2}(g)$$
For many years, both producer gas and water gas were used as fuels in industry and for domestic cooking. The large-scale preparation of these gases was carried out alternately, that is, first producer gas, then water gas, and so on. Using thermochemical reasoning, explain why this procedure was chosen.

Daniel Kim

Numerade Educator

Problem 91

Compare the heat produced by the complete combustion of 1 mole of methane $\left(\mathrm{CH}_{4}\right)$ with a mole of water gas $\left(0.50\right.$ mole $\mathrm{H}_{2}$ and 0.50 mole $\mathrm{CO}$ ) under the same conditions. On the basis of your answer, would you prefer methane over water gas as a fuel? Can you suggest two other reasons why methane is preferable to water gas as a fuel?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 92

The so-called hydrogen economy is based on hydrogen produced from water using solar energy. The gas may be burned as a fuel:
$$2 \mathrm{H}_{2}(g)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{H}_{2} \mathrm{O}(l)$$
A primary advantage of hydrogen as a fuel is that it is nonpolluting. A major disadvantage is that it is a gas and therefore is harder to store than liquids or solids. Calculate the volume of hydrogen gas at $25^{\circ} \mathrm{C}$ and 1.00 atm required to produce an amount of energy equivalent to that produced by the combustion of a gallon of octane $\left(\mathrm{C}_{8} \mathrm{H}_{18}\right) .$ The density of octane is $2.66 \mathrm{~kg} / \mathrm{gal},$ and its standard enthalpy of formation is $-249.9 \mathrm{~kJ} / \mathrm{mol}$.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 93

Ethanol $\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\right)$ and gasoline (assumed to be all octane, $\mathrm{C}_{8} \mathrm{H}_{18}$ ) are both used as automobile fuel. If gasoline is selling for $\$ 4.50 /$ gal, what would the price of ethanol have to be in order to provide the same amount of heat per dollar? The density and $\Delta H_{\mathrm{f}}^{\circ}$ of octane are $0.7025 \mathrm{~g} / \mathrm{mL}$ and $-249.9 \mathrm{~kJ} / \mathrm{mol}$
and of ethanol are $0.7894 \mathrm{~g} / \mathrm{mL}$ and $-277.0 \mathrm{~kJ} / \mathrm{mol}$, respectively. 1 gal $=3.785$ L.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 94

The combustion of what volume of ethane $\left(\mathrm{C}_{2} \mathrm{H}_{6}\right)$ measured at $23.0^{\circ} \mathrm{C}$ and $752 \mathrm{mmHg},$ would be required to heat $855 \mathrm{~g}$ of water from $25.0^{\circ} \mathrm{C}$ to $98.0^{\circ} \mathrm{C} ?$

Daniel Kim

Numerade Educator

Problem 95

If energy is conserved, how can there be an energy crisis?

Rachel Vallejo

Numerade Educator

Problem 96

The heat of vaporization of a liquid $\left(\Delta H_{\mathrm{vap}}\right)$ is the energy required to vaporize $1.00 \mathrm{~g}$ of the liquid at its boiling point. In one experiment, $60.0 \mathrm{~g}$ of liquid nitrogen (boiling point $-196^{\circ} \mathrm{C}$ ) are poured into a Styrofoam cup containing $2.00 \times 10^{2} \mathrm{~g}$ of water at $55.3^{\circ} \mathrm{C}$. Calculate the molar heat of vaporization of liquid nitrogen if the final temperature of the water is $41.0^{\circ} \mathrm{C}$.

Daniel Kim

Numerade Educator

Problem 97

Explain the cooling effect experienced when ethanol is rubbed on your skin, given that
$$\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}(l) \longrightarrow \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}(g) \quad \Delta H^{\circ}=42.2 \mathrm{~kJ} / \mathrm{mol}$$

Rachel Vallejo

Numerade Educator

Problem 98

For which of the following reactions does $\Delta H_{\mathrm{rxn}}^{\circ}=$ $\Delta H_{\mathrm{f}}^{\circ} ?$
(a) $\mathrm{H}_{2}(g)+\mathrm{S}($ rhombic $) \longrightarrow \mathrm{H}_{2} \mathrm{~S}(g)$
(b) C(diamond) $+\mathrm{O}_{2}(g) \longrightarrow \mathrm{CO}_{2}(g)$
(c) $\mathrm{H}_{2}(g)+\mathrm{CuO}(s) \longrightarrow \mathrm{H}_{2} \mathrm{O}(l)+\mathrm{Cu}(s)$
(d) $\mathrm{O}(g)+\mathrm{O}_{2}(g) \longrightarrow \mathrm{O}_{3}(g)$

Daniel Kim

Numerade Educator

Problem 99

Calculate the work done (in joules) when 1.0 mole of water is frozen at $0^{\circ} \mathrm{C}$ and 1.0 atm. The volumes of 1 mole of water and ice at $0^{\circ} \mathrm{C}$ are $0.0180 \mathrm{~L}$ and $0.0196 \mathrm{~L},$ respectively.

Anand Jangid

Numerade Educator

Problem 100

A quantity of 0.020 mole of a gas initially at $0.050 \mathrm{~L}$ and $20^{\circ} \mathrm{C}$ undergoes a constant-temperature expansion until its volume is $0.50 \mathrm{~L}$. Calculate the work done (in joules) by the gas if it expands (a) against a vacuum and (b) against a constant pressure of 0.20 atm.
(c) If the gas in (b) is allowed to expand unchecked until its pressure is equal to the external pressure, what would its final volume be before it stopped expanding, and what would be the work done?

Daniel Kim

Numerade Educator

Problem 101

Calculate the standard enthalpy of formation for diamond, given that
$$\begin{array}{l} \text { C(graphite) }+\mathrm{O}_{2}(g) \longrightarrow \mathrm{CO}_{2}(g) \\
\qquad \begin{aligned}
\Delta H^{\circ} &=-393.5 \mathrm{~kJ} / \mathrm{mol} \\
\mathrm{C}(\text { diamond })+\mathrm{O}_{2}(g) \longrightarrow & \mathrm{CO}_{2}(g) \\
\Delta H^{\circ} &=-395.4 \mathrm{~kJ} / \mathrm{mol}
\end{aligned}
\end{array}$$

Rachel Vallejo

Numerade Educator

Problem 102

(a) For most efficient use, refrigerator freezer compartments should be fully packed with food. What is the thermochemical basis for this recommendation?
(b) Starting at the same temperature, tea and coffee remain hot longer in a thermal flask than chicken noodle soup. Explain.

Rachel Vallejo

Numerade Educator

Problem 103

Calculate the standard enthalpy change for the fermentation process.

Pam Owens

Numerade Educator

Problem 104

Portable hot packs are available for skiers and people engaged in other outdoor activities in a cold climate. The air-permeable paper packet contains a mixture of powdered iron, sodium chloride, and other components, all moistened by a little water. The exothermic reaction that produces the heat is a very common one-the rusting of iron:
$$4 \mathrm{Fe}(s)+3 \mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{Fe}_{2} \mathrm{O}_{3}(s)$$
When the outside plastic envelope is removed, $\mathrm{O}_{2}$ molecules penetrate the paper, causing the reaction to begin. A typical packet contains $250 \mathrm{~g}$ of iron to warm your hands or feet for up to 4 hours. How much heat (in kJ) is produced by this reaction?

Anand Jangid

Numerade Educator

Problem 105

A person ate 0.50 pound of cheese (an energy intake of $4000 \mathrm{~kJ}$ ). Suppose that none of the energy was stored in his body. What mass (in grams) of water would he need to perspire in order to maintain his original temperature? (It takes $44.0 \mathrm{~kJ}$ to vaporize 1 mole of water.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 106

The total volume of the Pacific Ocean is estimated to be $7.2 \times 10^{8} \mathrm{~km}^{3}$. A medium-sized atomic bomb produces $1.0 \times 10^{15} \mathrm{~J}$ of energy upon explosion. Calculate the number of atomic bombs needed to
release enough energy to raise the temperature of the water in the Pacific Ocean by $1^{\circ} \mathrm{C}$.

Rachel Vallejo

Numerade Educator

Problem 107

A 19.2 -g quantity of dry ice (solid carbon dioxide) is allowed to sublime (evaporate) in an apparatus like the one shown in Figure $6.5 .$ Calculate the expansion work done against a constant external pressure of 0.995 atm and at a constant temperature of $22^{\circ} \mathrm{C}$. Assume that the initial volume of dry ice is negligible and that $\mathrm{CO}_{2}$ behaves like an ideal gas.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 108

The enthalpy of combustion of benzoic acid $\left(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COOH}\right)$ is commonly used as the standard for calibrating constant-volume bomb calorimeters; its value has been accurately determined to be $-3226.7 \mathrm{~kJ} / \mathrm{mol} .$ When $1.9862 \mathrm{~g}$ of benzoic acid are burned in a calorimeter, the temperature rises from $21.84^{\circ} \mathrm{C}$ to $25.67^{\circ} \mathrm{C} .$ What is the heat capacity of the bomb? (Assume that the quantity of water surrounding the bomb is exactly $2000 \mathrm{~g}$.)

Daniel Kim

Numerade Educator

Problem 109

The combustion of a $25.0-\mathrm{g}$ gaseous mixture of $\mathrm{H}_{2}$ and $\mathrm{CH}_{4}$ releases $2354 \mathrm{~kJ}$ of heat. Calculate the amounts of the gases in grams.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 110

Calcium oxide (CaO) is used to remove sulfur dioxide generated by coal-burning power stations:
$$2 \mathrm{CaO}(s)+2 \mathrm{SO}_{2}(g)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{CaSO}_{4}(s)$$
Calculate the enthalpy change for this process if $6.6 \times 10^{5} \mathrm{~g}$ of $\mathrm{SO}_{2}$ are removed by this process every day.

Daniel Kim

Numerade Educator

Problem 111

Glauber's salt, sodium sulfate decahydrate $\left(\mathrm{Na}_{2} \mathrm{SO}_{4} \cdot 10 \mathrm{H}_{2} \mathrm{O}\right),$ undergoes a phase transition
(that is, melting or freezing) at a convenient temperature of about $32^{\circ} \mathrm{C}$ :
$$\begin{array}{r}
\mathrm{Na}_{2} \mathrm{SO}_{4} \cdot 10 \mathrm{H}_{2} \mathrm{O}(s) \longrightarrow \mathrm{Na}_{2} \mathrm{SO}_{4} \cdot 10 \mathrm{H}_{2} \mathrm{O}(l) \\
\Delta H^{\circ}=74.4 \mathrm{~kJ} / \mathrm{mol}
\end{array}
$$
As a result, this compound is used to regulate the temperature in homes. It is placed in plastic bags in the ceiling of a room. During the day, the endothermic melting process absorbs heat from the surroundings, cooling the room. At night, it gives off heat as it freezes. Calculate the mass of Glauber's salt in kilograms needed to lower the temperature of air in a room by $8.2^{\circ} \mathrm{C}$ at 1.0 atm. The dimensions of the room are $2.80 \mathrm{~m} \times 10.6 \mathrm{~m}$ $\times 17.2 \mathrm{~m},$ the specific heat of air is $1.2 \mathrm{~J} / \mathrm{g} \cdot{ }^{\circ} \mathrm{C}$
and the molar mass of air may be taken as $29.0 \mathrm{~g} / \mathrm{mol}$

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 112

A balloon $16 \mathrm{~m}$ in diameter is inflated with helium at $18^{\circ} \mathrm{C}$. (a) Calculate the mass of He in the balloon, assuming ideal behavior. (b) Calculate the work done (in joules) during the inflation process if the atmospheric pressure is $98.7 \mathrm{kPa}$.

Daniel Kim

Numerade Educator

Problem 113

Acetylene $\left(\mathrm{C}_{2} \mathrm{H}_{2}\right)$ can be hydrogenated (reacting with hydrogen) first to ethylene $\left(\mathrm{C}_{2} \mathrm{H}_{4}\right)$ and then to ethane $\left(\mathrm{C}_{2} \mathrm{H}_{6}\right) .$ Starting with $1 \mathrm{~mole}$ of $\mathrm{C}_{2} \mathrm{H}_{2},$ label the diagram shown here analogous to Figure 6.10 . Use the data in Appendix 2 .

Anand Jangid

Numerade Educator

Problem 114

Calculate the $\Delta H^{\circ}$ for the reaction
$$\mathrm{Fe}^{3+}(a q)+3 \mathrm{OH}^{-}(a q) \longrightarrow \mathrm{Fe}(\mathrm{OH})_{3}(s)$$

Daniel Kim

Numerade Educator

Problem 115

An excess of zinc metal is added to $50.0 \mathrm{~mL}$ of a $0.100 M$ AgNO $_{3}$ solution in a constant-pressure calorimeter like the one pictured in Figure $6.9 .$ As a result of the reaction
$$\mathrm{Zn}(s)+2 \mathrm{Ag}^{+}(a q) \longrightarrow \mathrm{Zn}^{2+}(a q)+2 \mathrm{Ag}(s)$$
the temperature rises from $19.25^{\circ} \mathrm{C}$ to $22.17^{\circ} \mathrm{C}$. If the heat capacity of the calorimeter is $98.6 \mathrm{~J} /{ }^{\circ} \mathrm{C},$ calculate the enthalpy change for the above reaction on a molar basis. Assume that the density and specific heat of the solution are the same as those for water, and ignore the specific heats of the metals.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 116

(a) A person drinks four glasses of cold water $\left(3.0^{\circ} \mathrm{C}\right)$ every day. The volume of each glass is $2.5 \times 10^{2} \mathrm{~mL} .$ How much heat (in $\mathrm{kJ}$ ) does the body have to supply to raise the temperature of the water to $37^{\circ} \mathrm{C},$ the body temperature?
(b) How much heat would your body lose if you were to ingest $8.0 \times 10^{2} \mathrm{~g}$ of snow at $0^{\circ} \mathrm{C}$ to quench thirst? (The amount of heat necessary to melt snow is $6.01 \mathrm{~kJ} / \mathrm{mol} .$ )

Daniel Kim

Numerade Educator

Problem 117

A driver's manual states that the stopping distance quadruples as the speed doubles; that is, if it takes $30 \mathrm{ft}$ to stop a car moving at $25 \mathrm{mph}$ then it would take $120 \mathrm{ft}$ to stop a car moving at $50 \mathrm{mph}$. Justify this statement by using mechanics and the first law of thermodynamics. [Assume that when a car is stopped, its kinetic energy $\left(\frac{1}{2} m u^{2}\right)$ is totally converted to heat.]

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 118

At $25^{\circ} \mathrm{C},$ the standard enthalpy of formation of $\mathrm{HF}(a q)$ is given by $-320.1 \mathrm{~kJ} / \mathrm{mol} ;$ of $\mathrm{OH}^{-}(a q),$ it is
$-229.6 \mathrm{~kJ} / \mathrm{mol} ;$ of $\mathrm{F}^{-}(a q),$ it is $-329.1 \mathrm{~kJ} / \mathrm{mol} ;$ and
of $\mathrm{H}_{2} \mathrm{O}(l),$ it is $-285.8 \mathrm{~kJ} / \mathrm{mol} .$
(a) Calculate the standard enthalpy of neutralization of $\mathrm{HF}(a q)$
$$
\mathrm{HF}(a q)+\mathrm{OH}^{-}(a q) \longrightarrow \mathrm{F}^{-}(a q)+\mathrm{H}_{2} \mathrm{O}(l)
$$
(b) Using the value of $-56.2 \mathrm{~kJ}$ as the standard enthalpy change for the reaction
$$\mathrm{H}^{+}(a q)+\mathrm{OH}^{-}(a q) \longrightarrow \mathrm{H}_{2} \mathrm{O}(l)
$$calculate the standard enthalpy change for the reaction$$\mathrm{HF}(a q) \longrightarrow \mathrm{H}^{+}(a q)+\mathrm{F}^{-}(a q)
$$

Daniel Kim

Numerade Educator

Problem 119

Why are cold, damp air and hot, humid air more uncomfortable than dry air at the same temperatures? (The specific heats of water vapor and air are approximately $1.9 \mathrm{~J} / \mathrm{g} \cdot{ }^{\circ} \mathrm{C}$ and $1.0 \mathrm{~J} / \mathrm{g} \cdot{ }^{\circ} \mathrm{C},$ respec-
tively.)

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 120

From the enthalpy of formation for $\mathrm{CO}_{2}$ and the following information, calculate the standard enthalpy of formation for carbon monoxide (CO).
$$
\begin{aligned}
\mathrm{CO}(g)+\frac{1}{2} \mathrm{O}_{2}(g) & \longrightarrow \mathrm{CO}_{2}(g) \\
\Delta H^{\circ} &=-283.0 \mathrm{~kJ} / \mathrm{mol}
\end{aligned}
$$Why can't we obtain it directly by measuring the enthalpy of the following reaction?$$\mathrm{C}(\text { graphite })+\frac{1}{2} \mathrm{O}_{2}(g) \longrightarrow \mathrm{CO}(g)$$

Daniel Kim

Numerade Educator

Problem 121

A 46-kg person drinks 500 g of milk, which has a "caloric" value of approximately $3.0 \mathrm{~kJ} / \mathrm{g}$. If only 17 percent of the energy in milk is converted to mechanical work, how high (in meters) can the person climb based on this energy intake? [Hint: The work done in ascending is given by $m g h,$ where $m$ is the mass (in kilograms), $g$ the gravitational acceleration $\left(9.8 \mathrm{~m} / \mathrm{s}^{2}\right),$ and $h$ the height (in meters).]

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 122

The height of Niagara Falls on the American side is $51 \mathrm{~m}$
(a) Calculate the potential energy of $1.0 \mathrm{~g}$ of water at the top of the falls relative to the ground level. (b) What is the speed of the falling water if all of the potential energy is converted to kinetic energy?
(c) What would be the increase in temperature of the water if all the kinetic energy were converted to heat? (See Problem 6.121 for suggestions.)

Daniel Kim

Numerade Educator

Problem 123

In the nineteenth century two scientists named Dulong and Petit noticed that for a solid element, the product of its molar mass and its specific heat is approximately $25 \mathrm{~J} /{ }^{\circ} \mathrm{C}$. This observation, now called Dulong and Petit's law, was used to estimate the specific heat of metals. Verify the law for the metals listed in Table $6.2 .$ The law does not apply to one of the metals. Which one is it? Why?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 124

Determine the standard enthalpy of formation of ethanol $\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\right)$ from its standard enthalpy of combustion $(-1367.4 \mathrm{~kJ} / \mathrm{mol})$

Daniel Kim

Numerade Educator

Problem 125

Acetylene $\left(\mathrm{C}_{2} \mathrm{H}_{2}\right)$ and benzene $\left(\mathrm{C}_{6} \mathrm{H}_{6}\right)$ have the same empirical formula. In fact, benzene can be made from acetylene as follows:
$$
3 \mathrm{C}_{2} \mathrm{H}_{2}(g) \longrightarrow \mathrm{C}_{6} \mathrm{H}_{6}(l)
$$
The enthalpies of combustion for $\mathrm{C}_{2} \mathrm{H}_{2}$ and $\mathrm{C}_{6} \mathrm{H}_{6}$ are $-1299.4 \mathrm{~kJ} / \mathrm{mol}$ and $-3267.4 \mathrm{~kJ} / \mathrm{mol},$ respectively.
Calculate the standard enthalpies of formation of $\mathrm{C}_{2} \mathrm{H}_{2}$ and $\mathrm{C}_{6} \mathrm{H}_{6}$ and hence the enthalpy change for the formation of $\mathrm{C}_{6} \mathrm{H}_{6}$ from $\mathrm{C}_{2} \mathrm{H}_{2}$.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 126

Ice at $0^{\circ} \mathrm{C}$ is placed in a Styrofoam cup containing $361 \mathrm{~g}$ of a soft drink at $23^{\circ} \mathrm{C}$. The specific heat of the drink is about the same as that of water. Some ice remains after the ice and soft drink reach an equilibrium temperature of $0^{\circ} \mathrm{C}$. Determine the mass of ice that has melted. Ignore the heat capacity of the cup.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 127

After a dinner party, the host performed the following trick. First, he blew out one of the burning candles. He then quickly brought a lighted match to about 1 in above the wick. To everyone's surprise, the candle was relighted. Explain how the host was able to accomplish the task without touching the wick.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 128

How much heat is required to decompose $89.7 \mathrm{~g}$ of $\mathrm{NH}_{4} \mathrm{Cl} ?$

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 129

A gas company in Massachusetts charges $\$ 1.30$ for $15 \mathrm{ft}^{3}$ of natural gas $\left(\mathrm{CH}_{4}\right)$ measured at $20^{\circ} \mathrm{C}$ and 1.0 atm. Calculate the cost of heating $200 \mathrm{~mL}$ of water (enough to make a cup of coffee or tea) from $20^{\circ} \mathrm{C}$ to $100^{\circ} \mathrm{C}$. Assume that only 50 percent of the heat generated by the combustion is used to heat the water; the rest of the heat is lost to the surroundings.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 130

Calculate the internal energy of a Goodyear blimp filled with helium gas at $1.2 \times 10^{5} \mathrm{~Pa}$. The volume of the blimp is $5.5 \times 10^{3} \mathrm{~m}^{3}$. If all the energy were used to heat 10.0 tons of copper at $21^{\circ} \mathrm{C},$ calculate the final temperature of the metal. (Hint: See Section 5.7 for help in calculating the internal energy of a gas. 1 ton $=9.072 \times 10^{5} \mathrm{~g} .$

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 131

Decomposition reactions are usually endothermic, whereas combination reactions are usually exothermic. Give a qualitative explanation for these trends.

Pam Owens

Numerade Educator

Problem 132

Acetylene $\left(\mathrm{C}_{2} \mathrm{H}_{2}\right)$ can be made by reacting calcium carbide $\left(\mathrm{CaC}_{2}\right)$ with water. (a) Write an equation for the reaction. (b) What is the maximum amount of heat (in joules) that can be obtained from the combustion of acetylene, starting with $74.6 \mathrm{~g}$ of $\mathrm{CaC}_{2} ?$

Daniel Kim

Numerade Educator

Problem 133

The average temperature in deserts is high during the day but quite cool at night, whereas that in regions along the coastline is more moderate. Explain.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 134

When $1.034 \mathrm{~g}$ of naphthalene $\left(\mathrm{C}_{10} \mathrm{H}_{8}\right)$ are burned in a constant-volume bomb calorimeter at $298 \mathrm{~K}$, $41.56 \mathrm{~kJ}$ of heat are evolved. Calculate $\Delta U$ and $\Delta H$ for the reaction on a molar basis.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 135

From a thermochemical point of view, explain why a carbon dioxide fire extinguisher or water should not be used on a magnesium fire.

Jason Boomer

Numerade Educator

Problem 136

Calculate the $\Delta U$ for the following reaction at $298 \mathrm{~K}:$
$$2 \mathrm{H}_{2}(g)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{H}_{2} \mathrm{O}(l)$$

Daniel Kim

Numerade Educator

Problem 137

lime is a term that includes calcium oxide (CaO, also called quicklime) and calcium hydroxide $\left[\mathrm{Ca}(\mathrm{OH})_{2},\right.$ also called slaked lime $] .$ It is used in the steel industry to remove acidic impurities, in airpollution control to remove acidic oxides such as $\mathrm{SO}_{2}$, and in water treatment. Quicklime is made industrially by heating limestone $\left(\mathrm{CaCO}_{3}\right)$ above $2000^{\circ} \mathrm{C}:$
$$
\begin{array}{r}
\mathrm{CaCO}_{3}(s) \longrightarrow \mathrm{CaO}(s)+\mathrm{CO}_{2}(g) \\
\Delta H^{\circ}=177.8 \mathrm{~kJ} / \mathrm{mol}
\end{array}
$$ Slaked lime is produced by treating quicklime with water:
$$
\begin{array}{r}
\mathrm{CaO}(s)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{Ca}(\mathrm{OH})_{2}(s) \\
\Delta H^{\circ}=-65.2 \mathrm{~kJ} / \mathrm{mol}
\end{array}
$$
The exothermic reaction of quicklime with water and the rather small specific heats of both quicklime $\left(0.946 \mathrm{~J} / \mathrm{g} \cdot{ }^{\circ} \mathrm{C}\right)$ and slaked lime $\left(1.20 \mathrm{~J} / \mathrm{g} \cdot{ }^{\circ} \mathrm{C}\right)$ make
it hazardous to store and transport lime in vessels made of wood. Wooden sailing ships carrying lime would occasionally catch fire when water leaked into the hold. (a) If a $500-\mathrm{g}$ sample of water reacts with an equimolar amount of $\mathrm{CaO}$ (both at an initial temperature of $25^{\circ} \mathrm{C}$ ), what is the final temperature of the product, $\mathrm{Ca}(\mathrm{OH})_{2} ?$ Assume that the product absorbs all of the heat released in the reaction.
(b) Given that the standard enthalpies of formation of $\mathrm{CaO}$ and $\mathrm{H}_{2} \mathrm{O}$ are $-635.6 \mathrm{~kJ} / \mathrm{mol}$ and $-285.8 \mathrm{~kJ} / \mathrm{mol}$
respectively, calculate the standard enthalpy of formation of $\mathrm{Ca}(\mathrm{OH})_{2}$

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 138

A 4.117 -g impure sample of glucose $\left(\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}\right)$ was burned in a constant-volume calorimeter having a heat capacity of $19.65 \mathrm{~kJ} /{ }^{\circ} \mathrm{C}$. If the rise in temperature is $3.134^{\circ} \mathrm{C},$ calculate the percent by mass of the glucose in the sample. Assume that the impurities are unaffected by the combustion process. See Appendix 2 for thermodynamic data.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 139

Construct a table with the headings $q, w, \Delta U,$ and $\Delta H .$ For each of the following processes, deduce whether each of the quantities listed is positive $(+)$ negative $(-),$ or zero $(0) .$ (a) Freezing of benzene.
(b) Compression of an ideal gas at constant temperature. (c) Reaction of sodium with water. (d) Boiling liquid ammonia. (e) Heating a gas at constant volume. (f) Melting of ice.

Alexander Lorenzo

Alexander Lorenzo

Numerade Educator

Problem 140

The combustion of $0.4196 \mathrm{~g}$ of a hydrocarbon releases $17.55 \mathrm{~kJ}$ of heat. The masses of the products are $\mathrm{CO}_{2}=1.419 \mathrm{~g}$ and $\mathrm{H}_{2} \mathrm{O}=0.290 \mathrm{~g}$. (a) What is
the empirical formula of the compound? (b) If the approximate molar mass of the compound is $76 \mathrm{~g}$, calculate its standard enthalpy of formation.

Daniel Kim

Numerade Educator

Problem 141

Metabolic activity in the human body releases approximately $1.0 \times 10^{4} \mathrm{~kJ}$ of heat per day. Assuming the body is $50 \mathrm{~kg}$ of water, how much would the body temperature rise if it were an isolated system? How much water must the body eliminate as perspiration to maintain the normal body temperature $\left(98.6^{\circ} \mathrm{F}\right) ?$ Comment on your results. The heat of vaporization of water may be taken as $2.41 \mathrm{~kJ} / \mathrm{g}$.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 142

Give an example for each of the following situations:
(a) Adding heat to a system raises its temperature,
(b) adding heat to a system does not change (raise) its temperature, and (c) a system's temperature is changed even though no heat is added or removed from it.

Daniel Kim

Numerade Educator

Problem 143

From the following data, calculate the heat of solution for KI: $$
\begin{array}{ccccc}
& \mathrm{NaCl} & \text { NaI } & \text { KCl } & \text { KI } \\
\hline \begin{array}{c}
\text { Lattice energy } \\
(\mathrm{kJ} / \mathrm{mol})
\end{array} & 788 & 686 & 699 & 632 \\
\begin{array}{c}
\text { Heat of solution } \\
(\mathrm{kJ} / \mathrm{mol})
\end{array} & 4.0 & -5.1 & 17.2 & ? \\
\hline
\end{array}
$$

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 144

Starting at A, an ideal gas undergoes a cyclic process involving expansion and compression, as shown here. Calculate the total work done. Does your result support the notion that work is not a state function?

Daniel Kim

Numerade Educator

Problem 145

For reactions in condensed phases (liquids and solids), the difference between $\Delta H$ and $\Delta U$ is usually quite small. This statement holds for reactions carried out under atmospheric conditions. For certain geochemical processes, however, the external pressure may be so great that $\Delta H$ and $\Delta U$ can differ by a significant amount. A well-known example is the slow conversion of graphite to diamond under Earth's surface. Calculate $(\Delta H-\Delta U)$ for the conversion of 1 mole of graphite to 1 mole of diamond at a pressure of 50,000 atm. The densities of graphite and diamond are $2.25 \mathrm{~g} / \mathrm{cm}^{3}$ and $3.52 \mathrm{~g} / \mathrm{cm}^{3},$ respectively.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 146

The diagrams (a)-(d) represent various physical and chemical processes:
(a) $2 \mathrm{~A}(g) \longrightarrow \mathrm{A}_{2}(g) ;(\mathrm{b}) \mathrm{MX}(s) \longrightarrow$
$\mathrm{M}^{+}(a q)+\mathrm{X}^{-}(a q)$
(c) $\mathrm{AB}(g)+\mathrm{C}(g) \longrightarrow \mathrm{AC}(g)+$
$\mathrm{B}(g) ;$ (d) $\mathrm{B}(l) \longrightarrow \mathrm{B}(g) .$ Predict whether the situations shown are endothermic or exothermic. Explain why in some cases no clear conclusions can be made.

Anand Jangid

Numerade Educator

Problem 147

A 20.3-g sample of an unknown metal and a $28.5-\mathrm{g}$ sample of copper, both at $80.6^{\circ} \mathrm{C},$ are added to $100 \mathrm{~g}$ of water at $11.2^{\circ} \mathrm{C}$ in a constant-pressure calorimeter

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 148

For most biological processes, $\Delta H \approx \Delta U$. Explain.

Daniel Kim

Numerade Educator

Problem 149

Estimate the potential energy expended by an average adult male in going from the ground to the top floor of the Empire State Building using the staircase.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 150

The fastest serve in tennis is about $150 \mathrm{mph}$. Can the kinetic energy of a tennis ball traveling at this speed be sufficient to heat $1 \mathrm{~mL}$ of water by $30^{\circ} \mathrm{C} ?$

Daniel Kim

Numerade Educator

Problem 151

Can the total energy output of the sun in 1 second be sufficient to heat all of the ocean water on Earth to its boiling point?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 152

It has been estimated that 3 trillion standard cubic feet of methane is released into the atmosphere every year. Capturing that methane would provide a source of energy, and it would also remove a potent greenhouse gas from the atmosphere (methane is 25 times more effective at trapping heat than an equal number of molecules of carbon dioxide). Standard cubic feet is measured at $60^{\circ} \mathrm{F}$ and 1 atm. Determine the amount of energy that could be obtained by combustion of the methane that escapes each year.

Penny Riley

Numerade Educator

Problem 153

Biomass plants generate electricity from waste material such as wood chips. Some of these plants convert the feedstock to ethanol $\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\right)$ for later use as a fuel. (a) How many grams of ethanol can be produced from 1.0 ton of wood chips, if 85 percent of the carbon is converted to $\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH} ?$
(b) How much energy would be released by burning the ethanol obtained from 1.0 ton of wood chips?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 154

Suppose an automobile carried hydrogen gas in its fuel tank instead of gasoline. At what pressure would the hydrogen gas need to be kept for the tank to contain an equivalent amount of chemical energy as a tank of gasoline?

Dr. Satish Ingale

Dr. Satish Ingale

Numerade Educator

Problem 155

A press release announcing a new fuel-cell car to the public stated that hydrogen is "relatively cheap" and "some stations in California sell hydrogen for $\$ 5$ a kilogram. A kg has the same energy as a gallon of gasoline, so it's like paying $\$ 5$ a gallon. But you go two to three times as far on the hydrogen." Analyze this claim.

Averell Hause

Carnegie Mellon University

Problem 156

We hear a lot about how the burning of hydrocarbons produces the greenhouse gas $\mathrm{CO}_{2}$, but what about the effect of increasing energy consumption on the amount of oxygen in the atmosphere required to sustain life? The figure shows past and projected world energy consumption. (a) How many moles of oxygen would be required to generate the additional energy expenditure for the next decade? (b) What would be the resulting decrease in atmospheric oxygen?

Rajesh Singh

Numerade Educator