# Chemistry

## Educators

Problem 1

A burning match and a bonfire may have the same temperature, yet you would not sit around a burning match on a fall evening to stay warm. Why not?

Will L.

Problem 2

Prepare a table identifying several energy transitions that take during the typical operation of an automobile.

Problem 3

Explain the difference between heat capacity and specific heat of a substance.

Will L.

Problem 4

Calculate the heat capacity, in joules and in calories per degree, of the following:
(a) 28.4 g of water

Problem 5

Calculate the heat capacity, in joules and in calories per degree, of the following:
(a) 45.8 g of nitrogen gas
(b) 1.00 pound of aluminum metal

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Problem 6

How much heat, in joules and in calories, must be added to a $75.0-\mathrm{g}$ iron block with a specific heat of 0.449 $\mathrm{J} / \mathrm{g}$ $^{\circ} \mathrm{C}$ to increase its temperature from $25^{\circ} \mathrm{C}$ to its melting temperature of $1535^{\circ} \mathrm{C} ?$

Problem 7

How much heat, in joules and in calories, is required to heat a $28.4-\mathrm{g}(1-\mathrm{oz})$ ice cube from $-23.0^{\circ} \mathrm{C}$ to $-1.0^{\circ} \mathrm{C} ?$

Will L.

Problem 8

How much would the temperature of 275 g of water increase if 36.5 $\mathrm{kJ}$ of heat were added?

Problem 9

If 14.5 $\mathrm{kJ}$ of heat were added to 485 $\mathrm{g}$ of liquid water, how much would its temperature increase?

Will L.

Problem 10

A piece of unknown substance weighs 44.7 $\mathrm{g}$ and requires 2110 $\mathrm{J}$ to increase its temperature from $23.2^{\circ} \mathrm{C}$ to $89.6^{\circ} \mathrm{C}$
(a) What is the specific heat of the substance?
(b) If it is one of the substances found in Table $5.1,$ what is its likely identity?

Problem 11

A piece of unknown solid substance weighs $437.2 \mathrm{g},$ and requires 8460 $\mathrm{J}$ to increase its temperature from 19.3 $^\circ \mathrm{C}$ to $68.9^{\circ} \mathrm{C}$
(a) What is the specific heat of the substance?
(b) If it is one of the substances found in Table $5.1,$ what is its likely identity?

Will L.

Problem 12

An aluminum kettle weighs 1.05 $\mathrm{kg}$
(a) What is the heat capacity of the kettle?
(b) How much heat is required to increase the temperature of this kettle from $23.0^{\circ} \mathrm{C}$ to $99.0^{\circ} \mathrm{C} ?$
(c) How much heat is required to heat this kettle from $23.0^{\circ} \mathrm{C}$ if it contains 1.25 $\mathrm{L}$ of water (density of 0.997 $\mathrm{g} / \mathrm{mL}$ and a specific heat of 4.184 $\mathrm{J} / \mathrm{g}^{\circ} \mathrm{C}$ )?

Problem 13

Most people find waterbeds uncomfortable unless the water the waterature is maintained at about $85^{\circ} \mathrm{F}$ . Unless it is heated, a waterbed that contains 892 $\mathrm{L}$ of cools from $85^{\circ} \mathrm{F}$ to $72^{\circ} \mathrm{F}$ in 24 hours. Estimate the amount of electrical energy required over 24 hours, in kWh, to keep the bed from cooling. Note that 1 kilowatt-hour (kWh) =
$3.6 \times 10^{6} \mathrm{J},$ and assume that the density of water is 1.0 $\mathrm{g} / \mathrm{mL}$ (independent of temperature). What other assumptions did you make? How did they affect your calculated result (i.e., were they likely to yield positive or negative errors)?

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Problem 14

A 500 -mL bottle of water at room temperature and a 2 -L bottle of water at the same temperature were placed in a refrigerator. After 30 minutes, the 500 -mL bottle of water had coled to the temperature of the refrigerator. An hour later, the 2 -L of water had cooled to the same temperature. When asked which sample of water lost the most heat, one student replied that both bottles lost the same same amount of heat because they started at the same temperature and finished at the same temperature. A second student thought that the 2 -L bottle of water lost more heat because there was more water. A third student believed that the 500 -mL bottle of water lost more heat because it cooled more quickly. A fourth student thought that it was not possible to tell because we do not know the inperature and the final temperature of the water. Indicate which of these answers is correct and describe the error in each of the other answers.

Problem 15

Would the amount of heasured for the reaction in Example 5.5 be greater, or remain the same if
we used a calorimeter that was a poorer insulator than a colorimeter? Explain your answer.

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Problem 16

Would the amount of heat absorbed by the dissolution in Example 5.6 appear, or remain the
same if the experimenter used a calorimeter that was a poorer insulator than a coffee cup calorimeter? Explain your answer.

Problem 17

Would the amount of heat absorbed by the dissolution in Example 5.6 appear lesser, or remain the
same if the heat capacity of the calorimeter were taken into account? Explain your answer.

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Problem 18

How many milliliters of water a $23^{\circ} \mathrm{C}$ with a density of 1.00 $\mathrm{g} / \mathrm{mL}$ mixed with 180 $\mathrm{mL}$ (about 6 $\mathrm{oz} )$ of coffee at $95^{\circ} \mathrm{C}$ so that the resulting combination will have a temperature of $60^{\circ} \mathrm{C} ?$ Assume that coffee and water have the same density and the same specific heat.

Problem 19

How much will the temperature of a cup $(180 \mathrm{g})$ of coffee at $95^{\circ} \mathrm{C}$ be reduced when a 45 $\mathrm{g}$ silver spoon (specific heat 0.24 $\mathrm{Jg}^{\circ} \mathrm{C} )$ at $25^{\circ} \mathrm{C}$ is placed in the coffe and the two ared to reach the same temperature?
Assume that the coffee has the same density and specific heat as water.

Will L.

Problem 20

A $45-$ galuminum spoon (specific heat 0.88 $\mathrm{C} )$ at $24^{\circ} \mathrm{C}$ is placed in 180 $\mathrm{mL}(180 \mathrm{g})$ of coffee at $85^{\circ} \mathrm{C}$ and the temperature of the two become equal.
(a) What is the final temperature when the two become equal? Assume that coffee has the same specific heat as water.
(b) The first time a student solved this problem she got an answer of $88^{\circ}$ C. Explain why this is clearly an incorrect answer.

Problem 21

The temperature of the cooling water as it leaves the hot engine of an automobile is $240^{\circ} \mathrm{F}$ . After it passes through the radiator it has a temperature of $175^{\circ} \mathrm{F}$ . Calculate the amount of heat transferred from the engine to the surroundings by one gallon of water with a specific heat of 4.184 $\mathrm{J} / \mathrm{g}^{\circ} \mathrm{C}$ .

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Problem 22

A 70.0 -g piece of metal at $80.0^{\circ} \mathrm{C}$ is placed in 100 $\mathrm{g}$ of water at $22.0^{\circ} \mathrm{C}$ contained in a calorimeter like that shown in Figure 5.12 . The metal and water come to the same temperature at $24.6^{\circ} \mathrm{C}$ . How much heat did the metal
give up to the water? What is the specific heat of the metal?

Problem 23

If a reaction produces 1.506 $\mathrm{kJ}$ of heat, which is trapped in 30.0 $\mathrm{g}$ of water initially a6.5 $^{\circ} \mathrm{C}$ in a calorimeter like that in Figure $5.12,$ what is the resulting temperature of the water?

Will L.

Problem 24

A 0.500 -g sample of $\mathrm{KCl}$ is added to 50.0 $\mathrm{g}$ of water in a calorimeter (Figure 5.12$) .$ If the temperature decreases by $1.05^{\circ} \mathrm{C},$ what is the approximate amount of heat involved in the dissolution of the KCl, assuming the specific heat of the resulting solution is 4.18 $\mathrm{J} / \mathrm{g}^{\circ} \mathrm{C} ?$ Is the reaction exothermic or endothermic?

Problem 25

Dissolving 3.0 $\mathrm{g}$ of $\mathrm{CaCl}_{2}(s)$ in 150.0 $\mathrm{g}$ of water in a calorimeter (Figure 5.12$)$ at $22.4^{\circ} \mathrm{C}$ causes the temperature to rise to $25.8^{\circ} \mathrm{C}$ . What is the approximate amount of heat involved in the dissolution, assuming the
specific heat of the resulting solution is 4.18 $\mathrm{J} / \mathrm{g}^{\circ} \mathrm{C} ?$ Is the reacthermic or endothermic?

Will L.

Problem 26

When 50.0 $\mathrm{g}$ of 0.200 $\mathrm{M} \mathrm{NaCl}(a q)$ at $24.1^{\circ} \mathrm{C}$ is added to 100.0 $\mathrm{g}$ of 0.100 $\mathrm{M} \mathrm{AgNO}_{3}(a q)$ at $24.1^{\circ} \mathrm{C}$ in a calorimeter, the temperature increases to $25.2^{\circ} \mathrm{C}$ as AgCl(s) forms. Assuming the specific heat of the solution and products is 4.20 $\mathrm{J} / \mathrm{g}^{\circ} \mathrm{C}$ , calculate the approximate amount of heat in joules produced.

Problem 27

The addition of 3.15 g of $\mathrm{Ba}(\mathrm{OH})_{2} \cdot 8 \mathrm{H}_{2} \mathrm{O}$ to a solution of 1.52 $\mathrm{g}$ of $\mathrm{NH}_{4} \mathrm{SCN}$ in 100 $\mathrm{g}$ of water in a calorimeter caused the temperature to fall by $3.1^{\circ} \mathrm{C}$ . Assuming the specific heat of the solution and products is 4.20 $\mathrm{Jg}^{\circ} \mathrm{C}$ , calculate the approximate amount of heat absorbed by the reaction, which can be represented by the following equation:
$\mathrm{Ba}(\mathrm{OH})_{2} \cdot 8 \mathrm{H}_{2} \mathrm{O}(s)+2 \mathrm{NH}_{4} \mathrm{O} \mathrm{CN}(a q) \rightarrow \mathrm{Ba}(\mathrm{SCN})_{2}(a q)+2 \mathrm{NH}_{3}(a q)+10 \mathrm{H}_{2} \mathrm{O}(l)$

Will L.

Problem 28

The reaction of 50 $\mathrm{mL}$ of acid and 50 $\mathrm{mL}$ of base described in Example 5.5 increased the temperature of the solution by 6.9 degrees $\mathrm{C}$ . How much would the temperature have increased if 100 $\mathrm{mL}$ of acid and 100 $\mathrm{mL}$ of base had been used in the same calorimeter starting at the same temperature of $22.0^{\circ} \mathrm{C} ?$ Explain your answer.

Problem 29

If the 3.21 $\mathrm{g}$ of $\mathrm{NH}_{4} \mathrm{NO}_{3}$ in Example 5.6 were dissolved in 100.0 $\mathrm{g}$ of water under the same conditions, how much would the temperature change? Explain your answer.

Will L.

Problem 30

When 1.0 $\mathrm{g}$ of fructose, $\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}(s),$ a sugar commonly found in fruits, is burned in oxygen in a bomb calorimeter, the temperature of the calorimeter increases by $1.58^{\circ} \mathrm{C}$ . If the heat capacity of the calorimeter and its
contents is $9.90 \mathrm{kJ} /^{\prime} \mathrm{C},$ what is $q$ for this combustion?

Problem 31

When a 0.740 - g sample of trinitrotoluene (TNT), $\mathrm{C}_{7} \mathrm{H}_{5} \mathrm{N}_{2} \mathrm{O}_{6},$ is burned in a bomb calorimeter, the temperature increases from $23.4^{\circ} \mathrm{C}$ to $26.9^{\circ} \mathrm{C}$ . The heat capacity of the calorimeter is 534 $\mathrm{J}^{\prime} \mathrm{C}$ , and it contains 675 $\mathrm{mL}$ of water.
How much heat was produced by the combustion of the TNT sample?

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Problem 32

One method of generating electricity is by burning coal to heat water, which produces steam that drives an electric generator. To determine the rate at which coal is to be fed into the burner in this type of plant, the heat of combustion per ton of coal must be determined using a bomb calomb calorimeter. When 1.00 $\mathrm{g}$ of coal is burned in a bomb calorimeter (Figure 5.17 ), the temperature increases by $1.48^{\circ} \mathrm{C}$ . If the heat capacity of the calorimeter is 21.6 $\mathrm{kJ} /^{\circ} \mathrm{C},$ determine the heat produced by combustion of a ton of coal $\left(2.000 \times 10^{3} \mathrm{pounds}\right)$

Problem 33

The amount of fat recommended for someone with a daily diet of 2000 Calories is 65 $\mathrm{g}$ . What percent of the calories in this diet would be supplied by this amount of fat if the average number of Calories for fat is 9.1 Calories/g?

Will L.

Problem 34

A teaspoon of the carbohydrate sucrose (common sugar) contains 16 Calories $(16 \text { kcal). What is the mass of }$ one teaspoon of sucrose if the average number of Calories for carbohydrates is 4.1 Calories/g?

Problem 35

What is the maximum mass of carbohydrate in a 6-oz serving of diet soda that contains less than 1 Calorie per can if the average number of Calories for carbohydrates is 4.1 Calories/g?

Will L.

Problem 36

A pint of premium ice cream can contain 1100 Calories. What mass of fat, in grams and pounds, must be produced in the body to store an extra $1.1 \times 10^{3}$ Calories if the average number of Calories for fat is 9.1 Calories/g?

Problem 37

A serving of a breakfast cereal contains 3 $\mathrm{g}$ of protein, 18 $\mathrm{g}$ of carbohydrates, and 6 $\mathrm{g}$ of fat. What is the Calorie content of a serving of this cereal if the average number of Calories for fat is 9.1 Calories/g, for carbohydrates is 4.1 Calories/g, and for protein is 4.1 Calories/g?

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Problem 38

Which is the least expensive source of energy in kilojoules per dollar: a box of breakfast cereal that weighs 32 ounces and costs $\$ 4.23,$or a liter of isooctane (density, 0.6919$\mathrm{g} / \mathrm{mL} )$that costs$\$0.45 ?$ Compare the nutritional value of the cereal with the heat produced by combustion of the isooctane under standard conditions. A 1.0 -ounce serving of the cereal provides 130 Calories.

Problem 39

Explain how the heasured in Example 5.5 differs from the enthalpy change for the exothermic reaction described by the following equation: $\mathrm{HCl}(a q)+\mathrm{NaOH}(a q) \longrightarrow \mathrm{NaCl}(a q)+\mathrm{H}_{2} \mathrm{O}(l)$

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Problem 40

Using the data in the check your learning section of Example $5.5,$ calculate $\Delta H$ in $\mathrm{k} / \mathrm{mol}$ of $\mathrm{AgNO}_{3}(a q)$ for the reaction: $\operatorname{NaCl}(a q)+\operatorname{AgNO}_{3}(a q) \longrightarrow \operatorname{AgCl}(s)+\operatorname{NaNO}_{3}(a q)$

Problem 41

Calculate the enthalpy of solution $\left(\Delta H \text { for the dissolution) per mole of } \mathrm{NH}_{4} \mathrm{NO}_{3} \text { under the conditions described }\right.$
in Example $5.6 .$

Will L.

Problem 42

Calculate $\Delta H$ for the reaction described by the equation. (Hint: use the value for the approximate amount of heat absorbed by the reaction that you calculated in a previous exercise.)
$\mathrm{Ba}(\mathrm{OH})_{2} \cdot 8 \mathrm{H}_{2} \mathrm{O}(s)+2 \mathrm{NH}_{4} \mathrm{SCN}(a q) \longrightarrow \mathrm{Ba}(\mathrm{SCN})_{2}(a q)+2 \mathrm{NH}_{3}(a q)+10 \mathrm{H}_{2} \mathrm{O}(l)$

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Problem 43

Calculate the enthalpy of solution $\left(\Delta H \text { for the dissolution) per mole of } \mathrm{CaCl}_{2} \text { ( refer to exercise } 25\right)$

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Problem 44

Although the gas used in an oxyacetylene torch (Figure 5.7$)$ is essentially pure acetylene, the heat produced by combustion of one mole of actylene in such a torch is likely not equal to the enthalpy of combustion of acetylene listed in Table 5.2 . Considering the conditions for which the tabulated data are reported, suggest an explanation.

Problem 45

How much heat is produced by burning 4.00 moles of acetylene under standard state conditions?

Will L.

Problem 46

How much heat is produced by combustion of 125 $\mathrm{g}$ of methanol under standard state conditions?

Problem 47

How many moles of isooctane must be burned to produce 100 $\mathrm{kJ}$ of heat under standard state conditions?

Will L.

Problem 48

What mass of carbon monoxide must be burned to produce 175 $\mathrm{kJ}$ of heat under standard state conditions?

Problem 49

When 2.50 g of methane burns in oxygen, 125 $\mathrm{kJ}$ of heat is produced. What is the enthalpy of combustion per mole of methane under these conditions?

Will L.

Problem 50

How much heat is produced when 100 $\mathrm{mL}$ of 0.250 $\mathrm{M} \mathrm{HCl}(\text { density }, 1.00 \mathrm{g} / \mathrm{mL})$ and 200 $\mathrm{mL}$ of 0.150 $\mathrm{M} \mathrm{NaOH}$ (density, 1.00 $\mathrm{g} / \mathrm{mL} )$ are mixed?
$\mathrm{HCl}(a q)+\mathrm{NaOH}(a q) \longrightarrow \mathrm{NaCl}(a q)+\mathrm{H}_{2} \mathrm{O}(l) \quad \Delta H_{298}^{\circ}=-58 \mathrm{kJ}$
If both solutions are at the same temperature and the heat capacity of the products is $4.19 \mathrm{J} / \mathrm{g}^{\circ} \mathrm{C},$ how much will the temperature increase? What assumption did you make in your calculation?

Problem 51

A sample of 0.562 g of carbon is burned in oxygen in a bomb calorimeter, producing carbon dioxide. Assume both the reactants and products are under standard state conditions, and that the heat released is directly proportional to the enthalpy of combustion of graphite. The temperature of the calorimeter increases from $26.74^{\circ} \mathrm{C}$ to 27.93 ' What is the heat capacity of the calorimeter and its contents?

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Problem 52

Before the introduction of chlorofluorocarbons, sulfur dioxide (enthalpy of vaporization, 6.00 $\mathrm{kcal} / \mathrm{mol} )$ was used in household refrigerators. What mass of $\mathrm{SO}_{2}$ must be evaporated to remove as much heat as evaporation of
1.00 $\mathrm{kg}$ of $\mathrm{CCl}_{2} \mathrm{F}_{2}$ (enthalpy of vaporization is 17.4 $\mathrm{kJ} / \mathrm{mol} ) ?$ The vaporization reactions for $\mathrm{SO}_{2}$ and $\mathrm{CCl}_{2} \mathrm{F}_{2}$ are $\mathrm{SO}_{2}(l) \longrightarrow \mathrm{SO}_{2}(g)$ and $\mathrm{CCl}_{2} \mathrm{F}(l) \longrightarrow \mathrm{CCl}_{2} \mathrm{F}_{2}(g)$
respectively.

Problem 53

Homes may be heated by pumping hot water through radiators. What mass of water will provide the same amount of heat when coled from 95.0 to $35.0^{\circ} \mathrm{C}$ , as the heat provided when 100 $\mathrm{g}$ of steam is cooled from $110^{\circ} \mathrm{C}$ to $100^{\circ} \mathrm{C} .$

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Problem 54

Which of the enthalpies of combustion in Table 5.2 the table are also standard enthalpies of formation?

Problem 55

Does the standard enthalpy of formation of $\mathrm{H}_{2} \mathrm{O}(g)$ differ from $\Delta H^{\circ}$ for the reaction $2 \mathrm{H}_{2}(g)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{H}_{2} \mathrm{O}(g) ?$

Will L.

Problem 56

Joseph Priestly prepared oxygen in 1774 by heating red mercury(I) oxide with sunlight focused through a lens. How much heat is required to decompose exactly 1 mole of red $\mathrm{HgO}(s)$ to $\mathrm{Hg}(l)$ and $\mathrm{O}_{2}(g)$ under standard conditions?

Problem 57

How many kilojoules of heat will be released when exactly 1 mole of manganese, $\mathrm{Mn}$ , is burned to form $\mathrm{M} \mathrm{n}_{3} \mathrm{O}_{4}(\mathrm{s})$ at standard state condititions?

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Problem 58

How many kilojoules of heat will be released when exactly 1 mole of iron, Fe, is burned to form $\mathrm{Fe}_{2} \mathrm{O}_{3}(\mathrm{s})$ at standard state conditions?

Problem 59

The following sequence of reactions occurs in the commercial production of aqueous nitric acid:
$$4 \mathrm{NH}_{3}(g)+5 \mathrm{O}_{2}(g) \longrightarrow 4 \mathrm{NO}(g)+6 \mathrm{H}_{2} \mathrm{O}(l) \quad \Delta H=-907 \mathrm{kJ}$$
$$2 \mathrm{NO}(g)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{NO}_{2}(g) \quad \Delta H=-113 \mathrm{kJ}$$
$$3 \mathrm{NO}_{2}+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow 2 \mathrm{HNO}_{3}(a q)+\mathrm{NO}(g) \qquad \Delta H=-139 \mathrm{kJ}$$
Determine the total energy change for the production of one mole of aqueous nitric acid by this process.

Will L.

Problem 60

Both graphite and diamond burn.
$$\mathrm{C}(s, \text { diamond })+\mathrm{O}_{2}(g) \longrightarrow \mathrm{CO}_{2}(g)$$
For the conversion of graphite to diamond:
$$\mathrm{C}(s, \text { graphite }) \longrightarrow \mathrm{C}(s, \text { diamond }) \qquad \Delta H_{298}^{\circ}=1.90 \mathrm{kJ}$$
Which produces more heat, the combustion of graphite or the combustion of diamond?

Problem 61

From the molar heats of formation in Appendix $\mathrm{G}$ , determine how much heat is required to evaporate one mole of water: $\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{H}_{2} \mathrm{O}(g)$

Will L.

Problem 62

Which produces more heat?
$$\begin{array}{l}{\mathrm{Os}(s) \longrightarrow 2 \mathrm{O}_{2}(g) \longrightarrow \mathrm{OsO}_{4}(s)} \\ {\text { or }} \\ {\mathrm{Os}(s) \longrightarrow 2 \mathrm{O}_{2}(g) \longrightarrow \mathrm{OsO}_{4}(g)}\end{array}$$
for the phase change $\operatorname{OsO}_{4}(s) \longrightarrow \operatorname{OsO}_{4}(g) \qquad \Delta H=56.4 \mathrm{kJ}$

Problem 63

Calculate $\Delta H_{298}^{\circ}$ for the process
$$\mathrm{Sb}(s)+\frac{5}{2} \mathrm{Cl}_{2}(g) \longrightarrow \mathrm{SbCl}_{5}(s)$$
from the following information:
$$\begin{array}{ll}{\mathrm{Sb}(s)+\frac{3}{2} \mathrm{Cl}_{2}(g) \longrightarrow \operatorname{SbCl}_{3}(s)} & {\Delta H_{298}^{\circ}=-314 \mathrm{kJ}} \\ {\mathrm{SbCl}_{3}(s)+\mathrm{Cl}_{2}(g) \longrightarrow \mathrm{SbCl}_{5}(g)} & {\Delta H_{298}^{\circ}=-80 \mathrm{kJ}}\end{array}$$

Will L.

Problem 64

Calculate $\Delta H_{298}^{\circ}$ for the process $\mathrm{Zn}(s)+\mathrm{S}(s)+2 \mathrm{O}_{2}(g) \longrightarrow \mathrm{ZnSO}_{4}(s)$ from the following information:
$$\begin{array}{l}{\mathrm{Zn}(s)+\mathrm{S}(s) \longrightarrow \mathrm{ZnS}(s) \quad \Delta H_{298}^{\circ}=-206.0 \mathrm{kJ}} \\ {\mathrm{ZnS}(s)+2 \mathrm{O}_{2}(g) \longrightarrow \mathrm{ZnSO}_{4}(s) \quad \Delta H_{298}^{\circ}=-776.8 \mathrm{kJ}}\end{array}$$

Problem 65

Calculate $\Delta H$ for the process $\mathrm{Hg}_{2} \mathrm{Cl}_{2}(s) \longrightarrow 2 \mathrm{Hg}(l)+\mathrm{Cl}_{2}(g)$ from the following information:
$$\begin{array}{ll}{\operatorname{Hg}(l)+\mathrm{Cl}_{2}(g) \longrightarrow \operatorname{HgCl}_{2}(s)} & {\Delta H=-224 \mathrm{kJ}} \\ {\mathrm{Hg}(l)+\mathrm{HgCl}_{2}(s) \longrightarrow \mathrm{Hg}_{2} \mathrm{Cl}_{2}(s)} & {\Delta H=-41.2 \mathrm{kJ}}\end{array}$$

Will L.

Problem 66

Calculate $\Delta H_{298}^{\circ}$ for the process $\mathrm{Co}_{3} \mathrm{O}_{4}(s) \longrightarrow 3 \mathrm{Co}(s)+2 \mathrm{O}_{2}(g)$ from the following information:
$$\begin{array}{ll}{\mathrm{Co}(s)+\frac{1}{2} \mathrm{O}_{2}(g) \longrightarrow \mathrm{CoO}(s)} & {\Delta H_{298}^{\circ}=-237.9 \mathrm{kJ}} \\ {3 \mathrm{CoO}(s)+\frac{1}{2} \mathrm{O}_{2}(g) \longrightarrow \mathrm{Co}_{3} \mathrm{O}_{4}(s)} & {\Delta H_{298}^{\circ}=-177.5 \mathrm{kJ}}\end{array}$$

Problem 67

Calculate the standard molar enthalpy of formation of $\mathrm{NO}(g)$ from the following data:
$$\begin{array}{ll}{\mathrm{N}_{2}(g)+2 \mathrm{O}_{2} \longrightarrow 2 \mathrm{NO}_{2}(g)} & {\Delta H_{298}^{\mathrm{o}}=66.4 \mathrm{kJ}} \\ {2 \mathrm{NO}(g)+\mathrm{O}_{2} \longrightarrow 2 \mathrm{NO}_{2}(g)} & {\Delta H_{298}^{\circ}=-114.1 \mathrm{kJ}}\end{array}$$

Will L.

Problem 68

Using the data in Appendix G, calculate the standard enthalpy change for each of the following reactions:
$$\begin{array}{l}{\text { (a) } \mathrm{N}_{2}(g)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{NO}(g)} \\ {\text { (b) } \mathrm{Si}(s)+2 \mathrm{Cl}_{2}(g) \longrightarrow \mathrm{SiCl}_{4}(g)} \\ {\text { (c) } \mathrm{Fe}_{2} \mathrm{O}_{3}(s)+3 \mathrm{H}_{2}(g) \longrightarrow 2 \mathrm{Fe}(s)+3 \mathrm{H}_{2} \mathrm{O}(l)} \\ {\text { (d) } 2 \mathrm{LiOH}(s)+\mathrm{CO}_{2}(g) \longrightarrow \mathrm{Li}_{2} \mathrm{CO}_{3}(s)+\mathrm{H}_{2} \mathrm{O}(g)}\end{array}$$

Problem 69

Using the data in Appendix G, calculate the standard enthalpy change for each of the following reactions:
$$\begin{array}{l}{\text { (a) } \mathrm{Si}(s)+2 \mathrm{F}_{2}(g) \longrightarrow \mathrm{SiF}_{4}(g)} \\ {\text { (b) } 2 \mathrm{C}(s)+2 \mathrm{H}_{2}(g)+\mathrm{O}_{2}(g) \longrightarrow \mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{H}(l)} \\ {\text { (c) } \mathrm{CH}_{4}(g)+\mathrm{N}_{2}(g) \longrightarrow \mathrm{HCN}(g)+\mathrm{NH}_{3}(g)} \\ {\text { (d) } \mathrm{CS}_{2}(g)+3 \mathrm{Cl}_{2}(g) \longrightarrow \mathrm{CCl}_{4}(g)+\mathrm{S}_{2} \mathrm{Cl}_{2}(g)}\end{array}$$

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Problem 70

The following reactions can be used to prepare samples of metals. Determine the enthalpy change under standard state conditions for each.
$$\begin{array}{l}{\text { (a) } 2 \mathrm{Ag}_{2} \mathrm{O}(s) \longrightarrow 4 \mathrm{Ag}(s)+\mathrm{O}_{2}(g)} \\ {\text { (b) } \mathrm{SnO}(s)+\mathrm{CO}(g) \longrightarrow \mathrm{Sn}(s)+\mathrm{CO}_{2}(g)} \\ {\text { (c) } \mathrm{Cr}_{2} \mathrm{O}_{3}(s)+3 \mathrm{H}_{2}(g) \longrightarrow 2 \mathrm{Cr}(s)+3 \mathrm{H}_{2} \mathrm{O}(l)} \\ {\text { (d) } 2 \mathrm{Al}(s)+\mathrm{Fe}_{2} \mathrm{O}_{3}(s) \longrightarrow 2 \mathrm{l}_{2} \mathrm{O}_{3}(s)+2 \mathrm{Fe}(s)}\end{array}$$

Problem 71

The decomposition of hydrogen peroxide, $\mathrm{H}_{2} \mathrm{O}_{2},$ has been used to provide thrust in the control jets of various space vehicles. Using the data in Appendix $\mathrm{G}$ , determine how much heat is produced by the decomposition of exactly 1 mole of $\mathrm{H}_{2} \mathrm{O}_{2}$ under standard conditions.
$$2 \mathrm{H}_{2} \mathrm{O}_{2}(l) \longrightarrow 2 \mathrm{H}_{2} \mathrm{O}(g)+\mathrm{O}_{2}(g)$$

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Problem 72

Calculate the enthalpy of combustion of propane, $\mathrm{C}_{3} \mathrm{H}_{8}(g),$ for theformation of $\mathrm{H}_{2} \mathrm{O}(g)$ and $\mathrm{CO}_{2}(g) .$ The enthalpy of formation of propane is $-104 \mathrm{kJ} / \mathrm{mol}$ .

Problem 73

Calculate the enthalpy of combustion of butane, $\mathrm{C}_{4} \mathrm{H}_{10}(g)$ for the formation of $\mathrm{H}_{2} \mathrm{O}(g)$ and $\mathrm{CO}_{2}(g) .$ The enthalpy of formation of butane is $-126 \mathrm{kJ} / \mathrm{mol}$ .

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Problem 74

Both propane and butane are useous gaseous fuels. Which compound produces more heat per gram when burned?

Problem 75

The white pigment TiO $_{2}$ is prepared by the reaction of titanium tetrachloride, $\mathrm{TiCl}_{4}$with water vapor in the gas phase: TiCl $_{4}(g)+2 \mathrm{H}_{2} \mathrm{O}(g) \longrightarrow \mathrm{TiO}_{2}(s)+4 \mathrm{HCl}(g)$
How much heat is evolved in the production of exactly 1 mole of $\mathrm{T} \mathrm{O}_{2}(s)$ under standard state conditions?

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Problem 76

Water gas, a mixture of $\mathrm{H}_{2}$ and $\mathrm{CO}$ , is an important industrial fuel produced by the reaction of steam with red hot coke, essentially pure carbon: $\mathrm{C}(s)+\mathrm{H}_{2} \mathrm{O}(g) \rightarrow \mathrm{CO}(g)+\mathrm{H}_{2}(g)+\mathrm{H}_{2}(g)$
(a) Assuming that coke has the same enthalpy of formation as graphite, calculate $\Delta H_{298}^{\circ}$ for this reaction.
(b) Methanol, a liquid fuel that could possibly replace gasoline, can be prepared from water gas and additional hydrogen at high temperature and pressure in the presence of a suitable catalyst: $2 \mathrm{H}_{2}(g)+\mathrm{CO}(g) \longrightarrow \mathrm{CH}_{3} \mathrm{OH}(g)$ Under the conditions of the reaction, methanol forms as a gas. Calculate $\Delta H_{298}^{\circ}$ for this reaction and for the condensation of gaseous methanol to liquid methanol.
(c) Calculate the heat of combustion of 1 mole of liquid methanol to $\mathrm{H}_{2} \mathrm{O}(g)$ and $\mathrm{CO}_{2}(g) .$

Problem 77

In the early days of automobiles, illumination at night was provided by burning acetylene, $\mathrm{C}_{2} \mathrm{H}_{2}$ . Though no longer used as auto headlamps, acetylene is still used as a source of light by some cave explorers. The acetylene is (was) prepared in the lamp by the reaction of water with calcium carbide, $\mathrm{CaC}_{2}$ :
$$\mathrm{CaC}_{2}(s)+2 \mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{Ca}(\mathrm{OH})_{2}(s)+\mathrm{C}_{2} \mathrm{H}_{2}(g)$$
Calculate the standard enthalpy of the reaction. The $\Delta H_{\mathrm{f}}^{\circ}$ of $\mathrm{CaC}_{2}$ is $-15.14 \mathrm{kcal} / \mathrm{mol}$

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Problem 78

From the data in Table 5.2 , determine which of the following fuels produces the greatest amount of heat per gram when burned under standard conditions: $\mathrm{CO}(g), \mathrm{CH}_{4}(g),$ or $\mathrm{C}_{2} \mathrm{H}_{2}(g) .$

Problem 79

The enthalpy of combustion of hard coal averages $-35 \mathrm{kJ} / \mathrm{g}$ , that of gasoline, $1.28 \times 10^{5} \mathrm{kJ} / \mathrm{gal}$ . How many kilograms of hard coal provide the same amount of heat as is available from 1. 0 gallon of gasoline? Assume that the density of gasoline is 0.692 $\mathrm{g} / \mathrm{mL}$ (the same as the density of isooctane).

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Problem 80

Ethanol, $\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH},$ is used as a fuel for motor vehicles, particularly in Brazil
(a) Write the balanced equation for the combustion of ethanol to $\mathrm{CO}_{2}(g)$ and $\mathrm{H}_{2} \mathrm{O}(g),$ and, using the data in Appendix G, calculate the enthalpy of combustion of 1 mole of ethanol.
(b) The density of ethanol is 0.7893 $\mathrm{g} / \mathrm{mL}$ . Calculate the enthalpy of combustion of exactly 1 $\mathrm{L}$ of ethanol.
(c) Assuming that an automobile's mileage is directly proportional to the heat of combustion of the fuel, calculate how much farther an automobile could be expected to travel on 1 1 $\mathrm{L}$ of gasoline than on 1 of ethanol. Assume that gasoline has the heat of combustion and the density of n-octane, $\mathrm{C}_{8} \mathrm{H}_{18}\left(\Delta H_{\mathrm{f}}^{\circ}=-208.4 \mathrm{kJ} / \mathrm{mol} ; \text { density }=0.7025\right.$ $\mathrm{g} / \mathrm{mL}$ .

Problem 81

Among the substances that react with oxygen and that have been considered as potential rocket fuels are diborane $\left[\mathrm{B}_{2} \mathrm{H}_{6}, \text { produces } \mathrm{B}_{2} \mathrm{O}_{3}(\mathrm{s}) \text { and } \mathrm{H}_{2} \mathrm{O}(g)\right]$ , methane $\left[\mathrm{CH}_{4}, \text { produces } \mathrm{CO}_{2}(g) \text { and } \mathrm{H}_{2} \mathrm{O}(g)\right]$ , and hydrazine
$\left[\mathrm{N}_{2} \mathrm{H}_{4}, \text { produces } \mathrm{N}_{2}(g) \text { and } \mathrm{H}_{2} \mathrm{O}(g)\right] .$ On the basis of the heased by 1.00 $\mathrm{g}$ of each substance in its reaction with oxygen, which of these compounds offers the best possibility as a rocket fuel? The $\Delta H_{\mathrm{f}}^{\circ}$ of $\mathrm{B}_{2} \mathrm{H}_{6}(g), \mathrm{CH}_{4}(g)$
and $\mathrm{N}_{2} \mathrm{H}_{4}(l)$ may be found in Appendix G.

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Problem 82

How much heat is produced when 1.25 $\mathrm{g}$ of chromium metal reacts with oxygen gas under standard conditions?

Problem 83

Ethylene, $\mathrm{C}_{2} \mathrm{H}_{2},$ a byproduct from the fractional distillation of petroleum, is fourth among the 50 chemical compounds produced commercially in the largest quantities. About 80$\%$ of synthetic ethanol is manufactured from ethylene by its reaction with water in the presence of a suitable catalyst. $\mathrm{C}_{2} \mathrm{H}_{4}(g)+\mathrm{H}_{2} \mathrm{O}(g) \longrightarrow \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}(l)$ Using the data in the table in Appendix G, calculate $\Delta H^{\circ}$ for the reaction.

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Problem 84

The oxidation of the sugar glucose, $\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6},$ is described by the following equation:
$$\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}(s)+6 \mathrm{O}_{2}(g) \longrightarrow 6 \mathrm{CO}_{2}(g)+6 \mathrm{H}_{2} \mathrm{O}(l) \quad \Delta H=-2816 \mathrm{kJ}$$
The metabolism of glucose gives the same products, although the glucose reacts with oxygen in a series of steps in the body.
(a) How much heat in kilojoules can be produced by the metabolism of 1.0 $\mathrm{g}$ of glucose?
(b) How many Calories can be produced by the metabolism of 1.0 $\mathrm{g}$ of glucose?

Problem 85

Propane, $\mathrm{C}_{3} \mathrm{H}_{8},$ is a hydrocarbon that is commonly used as a fuel.
(a) Write a balanced equation for the complete combustion of propane gas.
(b) Calculate the volume of air at $25^{\circ} \mathrm{C}$ and 1.00 atmosphere that is needed to completely combletely combust 25.0 grams of propane. Assume that air is 21.0 percent $\mathrm{O}_{2}$ by volume. (Hint: we will see how to do this calculation in a later chapter on gases - for now use the information that 1.00 $\mathrm{L}$ of air at $25^{\circ} \mathrm{C}$ and 1.00 atm contains 0.275 $\mathrm{g}$ of $\mathrm{O}_{2}$ per liter.)
(c) The heat of combustion of propane is $-2,219.2 \mathrm{kJ} / \mathrm{mol}$ . Calculate the heat of formation, $\Delta H_{\mathrm{f}}^{\circ}$ of propane given that $\Delta H_{\mathrm{f}}^{\circ}$ of $\mathrm{H}_{2} \mathrm{O}(l)=-285.8 \mathrm{kJ} / \mathrm{mol}$ and $\Delta H_{\mathrm{f}}^{\circ}$ of $\mathrm{CO}_{2}(g)=-393.5 \mathrm{kJ} / \mathrm{mol} .$
(d) Assuming that all of the heased in burning 25.0 grams of propane is transferred to 4.00 kilograms of water, calculate the increase in temperature of the water.

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Problem 86

During a recent winter month in Sheboygan, Wisconsin, it was necessary to obtain 3500 $\mathrm{kWh}$ of heat provided by a natural gas furnace with 89$\%$ efficiency to keep a small house warm (the efficiency of a gas furnace is the percent of the heat produced by combustion that is transferred into the house).
(a) Assume that natural gas is pure methane and determine the volume of natural gas in cubic feet that was required to heat the house. The average temperature of the natural gas was $56^{\circ} \mathrm{F} ;$ at this temperature and a pressure of $1 \mathrm{atm},$ natural gas has a density of 0.681 $\mathrm{g} / \mathrm{L} .$
(b) How many gallons of LPG (liquefied petroled petrold be required to replace the natural gas used? Assume the LPG is liquid propane $\left[\mathrm{C}_{3} \mathrm{H}_{8} : \text { density }, 0.5318 \mathrm{g} / \mathrm{mL} ; \text { enthalpy of combustion, } 2219 \mathrm{kJ} / \mathrm{mol} \text { for the formation of }\right.$ $\mathrm{CO}_{2}(g)$ and $\mathrm{H}_{2} \mathrm{O}(l) ]$ and the furnace used to burn the LPG has the same efficiency as the gas furnace.
(c) What mass of carbon dioxide is produced by combustion of the methane used to heat the house?
(d) What mass of water is produced by combustion of the methane used to heat the house?
(e) What volume of air is required to provide the oxygen for the combustion of the methane used to heat the house? Air contains 23$\%$ oxygen by mass. The average density of air during the month was 1.22 $\mathrm{g} / \mathrm{L}$ .
(f) How many kilowat--hours $\left(1 \mathrm{kWh}=3.6 \times 10^{6} \mathrm{J}\right)$ of electricity would be required to heat necessary to heat the house? Note electricity is 100$\%$ efficient in producing heat inside a house.
(g) Although electricity is 100$\%$ efficient in producing heat inside a house, production and distribution of electricity is not 100$\%$ efficient. The efficiency of production and distribution of electricity produced in a coal-fired power plant is about 40$\%$ . A certain type of coal provides 2.26 $\mathrm{kWh}$ per pound upon combustion. What mass of this coal in kilograms will be required to produce the electrical energy necessary to heat the house if the efficiency of generation
and distribution is 40$\% ?$