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Chemistry | 12th Edition | ISBN: 9780078021510 | Authors: Raymond Chang; Kenneth Goldsby
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Author: Raymond Chang; Kenneth Goldsby
Publisher: McGraw-Hill Education
ISBN: 9780078021510
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Chapter 6 Problems

Chapter: 6 Problem: 6.1

Chemistry 12
Define these terms: system, surroundings, open system, closed system, isolated system, thermal energy, chemical energy, potential energy, kinetic energy, law of conservation of energy

Chapter: 6 Problem: 6.2

Chemistry 12
What is heat? How does heat differ from thermal energy? Under what condition is heat transferred from one system to another?

Chapter: 6 Problem: 6.3

Chemistry 12
What are the units for energy commonly employed in chemistry?

Chapter: 6 Problem: 6.4

Chemistry 12
A truck initially traveling at 60 km per hour is brought to a complete stop at a traffic light. Does this change violate the law of conservation of energy? Explain

Chapter: 6 Problem: 6.5

Chemistry 12
These are various forms of energy: chemical, heat, light, mechanical, and electrical. Suggest ways of interconverting these forms of energy

Chapter: 6 Problem: 6.6

Chemistry 12
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.

Chapter: 6 Problem: 6.7

Chemistry 12
Define these terms: thermochemistry, exothermic process, endothermic process.

Chapter: 6 Problem: 6.8

Chemistry 12
Stoichiometry is based on the law of conservation of mass. On what law is thermochemistry based?

Chapter: 6 Problem: 6.9

Chemistry 12
Describe two exothermic processes and two endothermic processes.

Chapter: 6 Problem: 6.1b

Chemistry 12
Decomposition reactions are usually endothermic, whereas combination reactions are usually exothermic. Give a qualitative explanation for these trends.

Chapter: 6 Problem: 6.11

Chemistry 12
On what law is the first law of thermodynamics based? Explain the sign conventions in the equation DU 5 q 1 w

Chapter: 6 Problem: 6.12

Chemistry 12
Explain what is meant by a state function. Give two examples of quantities that are state functions and two that are not.

Chapter: 6 Problem: 6.13

Chemistry 12
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

Chapter: 6 Problem: 6.14

Chemistry 12
Consider these changes. (a) Hg(l) Hg(g) (b) 3O2(g) 2O3(g) (c) CuSO4 ? 5H2O(s) CuSO4(s) 1 5H2O(g) (d) H2(g) 1 F2(g) 2HF(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?

Chapter: 6 Problem: 6.15

Chemistry 12
A sample of nitrogen gas expands in volume from 1.6 L to 5.4 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

Chapter: 6 Problem: 6.16

Chemistry 12
A gas expands in volume from 26.7 mL to 89.3 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.

Chapter: 6 Problem: 6.17

Chemistry 12
A gas expands and does P-V work on the surroundings equal to 325 J. At the same time, it absorbs 127 J of heat from the surroundings. Calculate the change in energy of the gas

Chapter: 6 Problem: 6.18

Chemistry 12
The work done to compress a gas is 74 J. As a result, 26 J of heat is given off to the surroundings. Calculate the change in energy of the gas

Chapter: 6 Problem: 6.19

Chemistry 12
Calculate the work done when 50.0 g of tin dissolves in excess acid at 1.00 atm and 258C: Sn(s) 1 2H1(aq) Sn21(aq) 1 H2(g) Assume ideal gas behavior.

Chapter: 6 Problem: 6.2b

Chemistry 12
Calculate the work done in joules when 1.0 mole of water vaporizes at 1.0 atm and 1008C. Assume that the volume of liquid water is negligible compared with that of steam at 1008C, and ideal gas behavior

Chapter: 6 Problem: 6.21

Chemistry 12
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?

Chapter: 6 Problem: 6.22

Chemistry 12
In writing thermochemical equations, why is it important to indicate the physical state (that is, gaseous, liquid, solid, or aqueous) of each substance?

Chapter: 6 Problem: 6.23

Chemistry 12
Explain the meaning of this thermochemical equation: 4NH3(g) 1 5O2(g) 4NO(g) 1 6H2O(g) H 5 2904 kJ/mol

Chapter: 6 Problem: 6.24

Chemistry 12
Consider this reaction: 2CH3OH(l) 1 3O2(g) 4H2O(l) 1 2CO2(g) H 5 21452.8 kJ/mol What is the value of DH 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 i

Chapter: 6 Problem: 6.25

Chemistry 12
The first step in the industrial recovery of zinc from the zinc sulfide ore is roasting, that is, the conversion of ZnS to ZnO by heating: 2ZnS(s) 1 3O2(g) 2ZnO(s) 1 2SO2(g) H 5 2879 kJ/mol Calculate the heat evolved (in kJ) per gram of ZnS roasted.

Chapter: 6 Problem: 6.26

Chemistry 12
Determine the amount of heat (in kJ) given off when 1.26 3 104 g of NO2 are produced according to the equation 2NO(g) 1 O2(g) 2NO2(g) H 5 2114.6 kJ/mol

Chapter: 6 Problem: 6.27

Chemistry 12
Consider the reaction 2H2O(g) 2H2(g) 1 O2(g) H 5 483.6 kJ/mol If 2.0 moles of H2O(g) are converted to H2(g) and O2(g) against a pressure of 1.0 atm at 1258C, what is DU for this reaction?

Chapter: 6 Problem: 6.28

Chemistry 12
Consider the reaction H2(g) 1 Cl2(g) 2HCl(g) H 5 2184.6 kJ/mol If 3 moles of H2 react with 3 moles of Cl2 to form HCl, calculate the work done (in joules) against a pressure of 1.0 atm at 258C. What is DU for this reaction? Assume the reaction goes to completion.

Chapter: 6 Problem: 6.29

Chemistry 12
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?

Chapter: 6 Problem: 6.3b

Chemistry 12
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?

Chapter: 6 Problem: 6.31

Chemistry 12
Consider the following data: 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 Cu to Al because Cu has a larger mass. (c) Heat will flow from Cu to Al because Cu has a la

Chapter: 6 Problem: 6.32

Chemistry 12
A piece of silver of mass 362 g has a heat capacity of 85.7 J/8C. What is the specific heat of silver?

Chapter: 6 Problem: 6.33

Chemistry 12
A 6.22-kg piece of copper metal is heated from 20.58C to 324.38C. Calculate the heat absorbed (in kJ) by the metal

Chapter: 6 Problem: 6.34

Chemistry 12
Calculate the amount of heat liberated (in kJ) from 366 g of mercury when it cools from 77.08C to 12.08C.

Chapter: 6 Problem: 6.35

Chemistry 12
A sheet of gold weighing 10.0 g and at a temperature of 18.08C is placed flat on a sheet of iron weighing 20.0 g and at a temperature of 55.68C. 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 t

Chapter: 6 Problem: 6.36

Chemistry 12
To a sample of water at 23.48C in a constant- pressure calorimeter of negligible heat capacity is added a 12.1-g piece of aluminum whose temperature is 81.78C. If the final temperature of water is 24.98C, calculate the mass of the water in the calorimeter. (Hint: See Table 6.2.)

Chapter: 6 Problem: 6.37

Chemistry 12
A 0.1375-g sample of solid magnesium is burned in a constant-volume bomb calorimeter that has a heat capacity of 3024 J/8C. The temperature increases by 1.1268C. Calculate the heat given off by the burning Mg, in kJ/g and in kJ/mol.

Chapter: 6 Problem: 6.38

Chemistry 12
A quantity of 85.0 mL of 0.900 M HCl is mixed with 85.0 mL of 0.900 M KOH in a constant-pressure calorimeter that has a heat capacity of 325 J/8C. If the initial temperatures of both solutions are the same at 18.248C, what is the final temperature of the mixed solution? The heat of neutralization is

Chapter: 6 Problem: 6.39

Chemistry 12
What is meant by the standard-state condition?

Chapter: 6 Problem: 6.4b

Chemistry 12
How are the standard enthalpies of an element and of a compound determined?

Chapter: 6 Problem: 6.41

Chemistry 12
What is meant by the standard enthalpy of a reaction?

Chapter: 6 Problem: 6.42

Chemistry 12
Write the equation for calculating the enthalpy of a reaction. Define all the terms.

Chapter: 6 Problem: 6.43

Chemistry 12
State Hesss law. Explain, with one example, the usefulness of Hesss law in thermochemistry.

Chapter: 6 Problem: 6.44

Chemistry 12
Describe how chemists use Hesss law to determine the DH8f of a compound by measuring its heat (enthalpy) of combustion.

Chapter: 6 Problem: 6.45

Chemistry 12
Which of the following standard enthalpy of formation values is not zero at 258C? Na(s), Ne(g), CH4(g), S8(s), Hg(l), H(g).

Chapter: 6 Problem: 6.46

Chemistry 12
The DH8f values of the two allotropes of oxygen, O2 and O3, are 0 and 142.2 kJ/mol, respectively, at 258C. Which is the more stable form at this temperature?

Chapter: 6 Problem: 6.47

Chemistry 12
Which is the more negative quantity at 258C: DH8f for H2O(l) or DH8f for H2O(g)?

Chapter: 6 Problem: 6.48

Chemistry 12
Predict the value of DH8f (greater than, less than, or equal to zero) for these elements at 258C: (a) Br2(g); Br2(l). (b) I2(g); I2(s).

Chapter: 6 Problem: 6.49

Chemistry 12
In general, compounds with negative DH8f values are more stable than those with positive DH8f values. H2O2(l) has a negative DH8f (see Table 6.4). Why, then, does H2O2(l) have a tendency to decompose to H2O(l) and O2(g)?

Chapter: 6 Problem: 6.5b

Chemistry 12
Suggest ways (with appropriate equations) that would enable you to measure the DH8f values of Ag2O(s) and CaCl2(s) from their elements. No calculations are necessary.

Chapter: 6 Problem: 6.51

Chemistry 12
Calculate the heat of decomposition for this process at constant pressure and 258C: CaCO3(s) CaO(s) 1 CO2(g) (Look up the standard enthalpy of formation of the reactant and products in Table 6.4.)

Chapter: 6 Problem: 6.52

Chemistry 12
The standard enthalpies of formation of ions in aqueous solutions are obtained by arbitrarily assigning a value of zero to H1 ions; that is, Hf[H1 (aq)] 5 0. (a) For the following reaction HCl(g) H2O H1(aq) 1 Cl2(aq) H 5 274.9 kJ/mol calculate DH8f for the Cl2 ions. (b) Given that DH8f for OH2 ions i

Chapter: 6 Problem: 6.53

Chemistry 12
Calculate the heats of combustion for the following reactions from the standard enthalpies of formation listed in Appendix 3: (a) 2H2(g) 1 O2(g) 2H2O(l) (b) 2C2H2(g) 1 5O2(g) 4CO2(g) 1 2H2O(l)

Chapter: 6 Problem: 6.54

Chemistry 12
Calculate the heats of combustion for the following reactions from the standard enthalpies of formation listed in Appendix 3: (a) C2H4(g) 1 3O2(g) 2CO2(g) 1 2H2O(l) (b) 2H2S(g) 1 3O2(g) 2H2O(l) 1 2SO2(g)

Chapter: 6 Problem: 6.55

Chemistry 12
Methanol, ethanol, and n-propanol are three common alcohols. When 1.00 g of each of these alcohols is burned in air, heat is liberated as shown by the following data: (a) methanol (CH3OH), 222.6 kJ; (b) ethanol (C2H5OH), 229.7 kJ; (c) n-propanol (C3H7OH), 233.4 kJ. Calculate the heats of combustion o

Chapter: 6 Problem: 6.56

Chemistry 12
The standard enthalpy change for the following reaction is 436.4 kJ/mol: H2(g) H(g) 1 H(g) Calculate the standard enthalpy of formation of atomic hydrogen (H).

Chapter: 6 Problem: 6.57

Chemistry 12
From the standard enthalpies of formation, calculate DH8rxn for the reaction C6H12(l) 1 9O2(g) 6CO2(g) 1 6H2O(l) For C6H12(l), Hf 5 2151.9 kJ/mol

Chapter: 6 Problem: 6.58

Chemistry 12
Pentaborane-9, B5H9, is a colorless, highly reactive liquid that will burst into flame when exposed to oxygen. The reaction is 2B5H9(l) 1 12O2(g) 5B2O3(s) 1 9H2O(l) Calculate the kilojoules of heat released per gram of the compound reacted with oxygen. The standard enthalpy of formation of B5H9 is 7

Chapter: 6 Problem: 6.59

Chemistry 12
Determine the amount of heat (in kJ) given off when 1.26 3 104 g of ammonia are produced according to the equation N2(g) 1 3H2(g) 2NH3(g) Hrxn 5 292.6 kJ/mol Assume that the reaction takes place under standardstate conditions at 258C.

Chapter: 6 Problem: 6.6b

Chemistry 12
At 8508C, CaCO3 undergoes substantial decomposition to yield CaO and CO2. Assuming that the DH8f values of the reactant and products are the same at 8508C as they are at 258C, calculate the enthalpy change (in kJ) if 66.8 g of CO2 are produced in one reaction.

Chapter: 6 Problem: 6.61

Chemistry 12
From these data, S(rhombic) 1 O2(g) SO2(g) Hrxn 5 2296.06 kJ/mol S(monoclinic) 1 O2(g) SO2(g) Hrxn 5 2296.36 kJ/mol calculate the enthalpy change for the transformation S(rhombic) S(monoclinic) (Monoclinic and rhombic are different allotropic forms of elemental sulfur.)

Chapter: 6 Problem: 6.62

Chemistry 12
From the following data, C(graphite) 1 O2(g) CO2(g) Hrxn 5 2393.5 kJ/mol H2(g) 1 1 2O2(g) H2O(l) Hrxn 5 2285.8 kJ/mol 2C2H6(g) 1 7O2(g) 4CO2(g) 1 6H2O(l) Hrxn 5 23119.6 kJ/mol calculate the enthalpy change for the reaction 2C(graphite) 1 3H2(g) C2H6(g)

Chapter: 6 Problem: 6.63

Chemistry 12
From the following heats of combustion, CH3OH(l) 1 3 2O2(g) CO2(g) 1 2H2O(l) Hrxn 5 2726.4 kJ/mol C(graphite) 1 O2(g) CO2(g) Hrxn 5 2393.5 kJ/mol H2(g) 1 1 2O2(g) H2O(l) Hrxn 5 2285.8 kJ/mol calculate the enthalpy of formation of methanol (CH3OH) from its elements: C(graphite) 1 2H2(g) 1 1 2O2(g)

Chapter: 6 Problem: 6.64

Chemistry 12
Calculate the standard enthalpy change for the reaction 2Al(s) 1 Fe2O3(s) 2Fe(s) 1 Al2O3(s) given that 2Al(s) 1 3 2O2(g) Al2O3(s) Hrxn 5 21669.8 kJ/mol 2Fe(s) 1 3 2O2(g) Fe2O3(s) Hrxn 5 2822.2 kJ/mol

Chapter: 6 Problem: 6.65

Chemistry 12
Define the following terms: enthalpy of solution, heat of hydration, lattice energy, heat of dilution.

Chapter: 6 Problem: 6.66

Chemistry 12
Why is the lattice energy of a solid always a positive quantity? Why is the hydration of ions always a negative quantity?

Chapter: 6 Problem: 6.67

Chemistry 12
Consider two ionic compounds A and B. A has a larger lattice energy than B. Which of the two compounds is more stable?

Chapter: 6 Problem: 6.68

Chemistry 12
Mg21 is a smaller cation than Na1 and also carries more positive charge. Which of the two species has a larger hydration energy (in kJ/mol)? Explain.

Chapter: 6 Problem: 6.69

Chemistry 12
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 th

Chapter: 6 Problem: 6.7b

Chemistry 12
Why is it dangerous to add water to a concentrated acid such as sulfuric acid in a dilution process?

Chapter: 6 Problem: 6.71

Chemistry 12
Which of the following does not have DH8f 5 0 at 258C? He(g) Fe(s) Cl(g) S8(s) O2(g) Br2(l)

Chapter: 6 Problem: 6.72

Chemistry 12
Calculate the expansion work done when 3.70 moles of ethanol are converted to vapor at its boiling point (78.38C) and 1.0 atm

Chapter: 6 Problem: 6.73

Chemistry 12
The convention of arbitrarily assigning a zero enthalpy value for the most stable form of each element in the standard state at 258C is a convenient way of dealing with enthalpies of reactions. Explain why this convention cannot be applied to nuclear reactions.

Chapter: 6 Problem: 6.74

Chemistry 12
Given the thermochemical equations: Br2(l) 1 F2(g) 2BrF(g) H 5 2188 kJ/mol Br2(l) 1 3F2(g) 2BrF3(g) H 5 2768 kJ/mol calculate the DH8rxn for the reaction BrF(g) 1 F2(g) BrF3(g)

Chapter: 6 Problem: 6.75

Chemistry 12
The standard enthalpy change DH8 for the thermal decomposition of silver nitrate according to the following equation is 178.67 kJ: AgNO3(s) AgNO2(s) 1 1 2O2(g) The standard enthalpy of formation of AgNO3(s) is 2123.02 kJ/mol. Calculate the standard enthalpy of formation of AgNO2(s).

Chapter: 6 Problem: 6.76

Chemistry 12
Hydrazine, N2H4, decomposes according to the following reaction: 3N2H4(l) 4NH3(g) 1 N2(g) (a) Given that the standard enthalpy of formation of hydrazine is 50.42 kJ/mol, calculate DH8 for its decomposition. (b) Both hydrazine and ammonia burn in oxygen to produce H2O(l) and N2(g). Write balanced e

Chapter: 6 Problem: 6.77

Chemistry 12
A quantity of 2.00 3 102 mL of 0.862 M HCl is mixed with an equal volume of 0.431 M Ba(OH)2 in a constant-pressure calorimeter of negligible heat capacity. The initial temperature of the HCl and Ba(OH)2 solutions is the same at 20.488C, For the process H1(aq) 1 OH2(aq) H2O(l) the heat of neutralizat

Chapter: 6 Problem: 6.78

Chemistry 12
A 3.53-g sample of ammonium nitrate (NH4NO3) was added to 80.0 mL of water in a constantpressure calorimeter of negligible heat capacity. As a result, the temperature of the water decreased from 21.68C to 18.18C. Calculate the heat of solution (DHsoln) of ammonium nitrate.

Chapter: 6 Problem: 6.79

Chemistry 12
Consider the reaction N2(g) 1 3H2(g) 2NH3(g) Hrxn 5 292.6 kJ/mol If 2.0 moles of N2 react with 6.0 moles of H2 to form NH3, calculate the work done (in joules) against a pressure of 1.0 atm at 258C. What is DU for this reaction? Assume the reaction goes to completion

Chapter: 6 Problem: 6.8b

Chemistry 12
Calculate the heat released when 2.00 L of Cl2(g) with a density of 1.88 g/L react with an excess of sodium metal at 258C and 1 atm to form sodium chloride.

Chapter: 6 Problem: 6.81

Chemistry 12
Venuss atmosphere is composed of 96.5 percent CO2, 3.5 percent N2, and 0.015 percent SO2 by volume. Its standard atmospheric pressure is 9.0 3 106 Pa. Calculate the partial pressures of the gases in pascals.

Chapter: 6 Problem: 6.82

Chemistry 12
A 2.10-mole sample of crystalline acetic acid, initially at 17.08C, is allowed to melt at 17.08C and is then heated to 118.18C (its normal boiling point) at 1.00 atm. The sample is allowed to vaporize at 118.18C and is then rapidly quenched to 17.08C, so that it recrystallizes. Calculate DH8 for the

Chapter: 6 Problem: 6.83

Chemistry 12
Calculate the work done in joules by the reaction 2Na(s) 1 2H2O(l) 2NaOH(aq) 1 H2(g) when 0.34 g of Na reacts with water to form hydrogen gas at 08C and 1.0 atm.

Chapter: 6 Problem: 6.84

Chemistry 12
You are given the following data: H2(g) 2H(g) H 5 436.4 kJ/mol Br2(g) 2Br(g) H 5 192.5 kJ/mol H2(g) 1 Br2(g) 2HBr(g) H 5 272.4 kJ/mol Calculate DH8 for the reaction H(g) 1 Br(g) HBr(g)

Chapter: 6 Problem: 6.85

Chemistry 12
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 19.48C and 2.23 atm, is burned in air. Calculate the heat released.

Chapter: 6 Problem: 6.86

Chemistry 12
When 2.740 g of Ba reacts with O2 at 298 K and 1 atm to form BaO, 11.14 kJ of heat are released. What is DH8f for BaO?

Chapter: 6 Problem: 6.87

Chemistry 12
Methanol (CH3OH) 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: 2CH3OH(l) 1 3O2(g) 2CO2(g) 1 4H2O(l) Hrxn 5 21452.8 kJ/mol

Chapter: 6 Problem: 6.88

Chemistry 12
A 44.0-g sample of an unknown metal at 99.08C was placed in a constant-pressure calorimeter containing 80.0 g of water at 24.08C. The final temperature of the system was found to be 28.48C. Calculate the specific heat of the metal. (The heat capacity of the calorimeter is 12.4 J/8C.)

Chapter: 6 Problem: 6.89

Chemistry 12
Using the data in Appendix 3, calculate the enthalpy change for the gaseous reaction shown here. (Hint: First determine the limiting reagent.) CO NO CO2 N2

Chapter: 6 Problem: 6.9b

Chemistry 12
Producer gas (carbon monoxide) is prepared by passing air over red-hot coke: C(s) 1 1 2O2(g) CO(g) Water gas (mixture of carbon monoxide and hydrogen) is prepared by passing steam over red-hot coke: C(s) 1 H2O(g) CO(g) 1 H2(g) For many years, both producer gas and water gas were used as fuels in in

Chapter: 6 Problem: 6.91

Chemistry 12
Compare the heat produced by the complete combustion of 1 mole of methane (CH4) with a mole of water gas (0.50 mole H2 and 0.50 mole 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 preferab

Chapter: 6 Problem: 6.92

Chemistry 12
The so-called hydrogen economy is based on hydrogen produced from water using solar energy. The gas may be burned as a fuel: 2H2(g) 1 O2(g) 2H2O(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 liq

Chapter: 6 Problem: 6.93

Chemistry 12
Ethanol (C2H5OH) and gasoline (assumed to be all octane, C8H18) 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 DH8f of octane are 0.7025 g/mL and 2249.9 kJ/mol a

Chapter: 6 Problem: 6.94

Chemistry 12
The combustion of what volume of ethane (C2H6), measured at 23.08C and 752 mmHg, would be required to heat 855 g of water from 25.08C to 98.08C?

Chapter: 6 Problem: 6.95

Chemistry 12
If energy is conserved, how can there be an energy crisis?

Chapter: 6 Problem: 6.96

Chemistry 12
The heat of vaporization of a liquid (DHvap) is the energy required to vaporize 1.00 g of the liquid at its boiling point. In one experiment, 60.0 g of liquid nitrogen (boiling point 21968C) are poured into a Styrofoam cup containing 2.00 3 102 g of water at 55.38C. Calculate the molar heat of vapori

Chapter: 6 Problem: 6.97

Chemistry 12
Explain the cooling effect experienced when ethanol is rubbed on your skin, given that C2H5OH(l) C2H5OH(g) H 5 42.2 kJ/mol

Chapter: 6 Problem: 6.98

Chemistry 12
For which of the following reactions does DH8rxn 5 DH8f ? (a) H2(g) 1 S(rhombic) H2S(g) (b) C(diamond) 1 O2(g) CO2(g) (c) H2(g) 1 CuO(s) H2O(l) 1 Cu(s) (d) O(g) 1 O2(g) O3(g)

Chapter: 6 Problem: 6.99

Chemistry 12
Calculate the work done (in joules) when 1.0 mole of water is frozen at 08C and 1.0 atm. The volumes of one mole of water and ice at 08C are 0.0180 L and 0.0196 L, respectively.

Chapter: 6 Problem: 6.1c

Chemistry 12
A quantity of 0.020 mole of a gas initially at 0.050 L and 208C undergoes a constant-temperature expansion until its volume is 0.50 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

Chapter: 6 Problem: 6.101

Chemistry 12
Calculate the standard enthalpy of formation for diamond, given that C(graphite) 1 O2(g) CO2(g) H 5 2393.5 kJ/mol C(diamond) 1 O2(g) CO2(g) H 5 2395.4 kJ/mol

Chapter: 6 Problem: 6.102

Chemistry 12
(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.

Chapter: 6 Problem: 6.103

Chemistry 12
Calculate the standard enthalpy change for the fermentation process. (See Problem 3.72.)

Chapter: 6 Problem: 6.104

Chemistry 12
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

Chapter: 6 Problem: 6.105

Chemistry 12
A person ate 0.50 pound of cheese (an energy intake of 4000 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 kJ to vaporize 1 mole of water.)

Chapter: 6 Problem: 6.106

Chemistry 12
The total volume of the Pacific Ocean is estimated to be 7.2 3 108 km3 . A medium-sized atomic bomb produces 1.0 3 1015 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 18C.

Chapter: 6 Problem: 6.107

Chemistry 12
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 228C. Assume that the initial volume of dry ice

Chapter: 6 Problem: 6.108

Chemistry 12
The enthalpy of combustion of benzoic acid (C6H5COOH) is commonly used as the standard for calibrating constant-volume bomb calorimeters; its value has been accurately determined to be 23226.7 kJ/mol. When 1.9862 g of benzoic acid are burned in a calorimeter, the temperature rises from 21.848C to 25.

Chapter: 6 Problem: 6.109

Chemistry 12
The combustion of a 25.0-g gaseous mixture of H2 and CH4 releases 2354 kJ of heat. Calculate the amounts of the gases in grams.

Chapter: 6 Problem: 6.11c

Chemistry 12
Calcium oxide (CaO) is used to remove sulfur dioxide generated by coal-burning power stations: 2CaO(s) 1 2SO2(g) 1 O2(g) 2CaSO4(s) Calculate the enthalpy change for this process if 6.6 3 105 g of SO2 are removed by this process every day.

Chapter: 6 Problem: 6.111

Chemistry 12
Glaubers salt, sodium sulfate decahydrate (Na2SO4 ? 10H2O), undergoes a phase transition (that is, melting or freezing) at a convenient temperature of about 328C: Na2SO4 ? 10H2O(s) Na2SO4 ? 10H2O(l) H 5 74.4 kJ/mol As a result, this compound is used to regulate the temperature in homes. It is placed

Chapter: 6 Problem: 6.112

Chemistry 12
A balloon 16 m in diameter is inflated with helium at 188C. (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 kPa.

Chapter: 6 Problem: 6.113

Chemistry 12
Acetylene (C2H2) can be hydrogenated (reacting with hydrogen) first to ethylene (C2H4) and then to ethane (C2H6). Starting with one mole of C2H2, label the diagram shown here analogous to Figure 6.10. Use the data in Appendix 3. Enthalpy

Chapter: 6 Problem: 6.114

Chemistry 12
Calculate the DH8 for the reaction Fe31(aq) 1 3OH2(aq) Fe(OH)3(s)

Chapter: 6 Problem: 6.115

Chemistry 12
An excess of zinc metal is added to 50.0 mL of a 0.100 M AgNO3 solution in a constant-pressure calorimeter like the one pictured in Figure 6.9. As a result of the reaction Zn(s) 1 2Ag1(aq) Zn21(aq) 1 2Ag(s) the temperature rises from 19.258C to 22.178C. If the heat capacity of the calorimeter is

Chapter: 6 Problem: 6.116

Chemistry 12
(a) A person drinks four glasses of cold water (3.08C) every day. The volume of each glass is 2.5 3 102 mL. How much heat (in kJ) does the body have to supply to raise the temperature of the water to 378C, the body temperature? (b) How much heat would your body lose if you were to ingest 8.0 3 102 g

Chapter: 6 Problem: 6.117

Chemistry 12
A drivers manual states that the stopping distance quadruples as the speed doubles; that is, if it takes 30 ft to stop a car moving at 25 mph then it would take 120 ft to stop a car moving at 50 mph. Justify this statement by using mechanics and the first law of thermodynamics. [Assume that when a ca

Chapter: 6 Problem: 6.118

Chemistry 12
At 258C, the standard enthalpy of formation of HF(aq) is given by 2320.1 kJ/mol; of OH2(aq), it is 2229.6 kJ/mol; of F2(aq), it is 2329.1 kJ/mol; and of H2O(l), it is 2285.8 kJ/mol. (a) Calculate the standard enthalpy of neutralization of HF(aq): HF(aq) 1 OH2(aq) F2(aq) 1 H2O(l) (b) Using the value

Chapter: 6 Problem: 6.119

Chemistry 12
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 J/g ? 8C and 1.0 J/g ? 8C, respectively.)

Chapter: 6 Problem: 6.12c

Chemistry 12
From the enthalpy of formation for CO2 and the following information, calculate the standard enthalpy of formation for carbon monoxide (CO). CO(g) 1 1 2O2(g) CO2(g) H 5 2283.0 kJ/mol Why cant we obtain it directly by measuring the enthalpy of the following reaction? C(graphite) 1 1 2O2(g) CO(g)

Chapter: 6 Problem: 6.121

Chemistry 12
A 46-kg person drinks 500 g of milk, which has a caloric value of approximately 3.0 kJ/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 mgh, where m is the

Chapter: 6 Problem: 6.122

Chemistry 12
The height of Niagara Falls on the American side is 51 m. (a) Calculate the potential energy of 1.0 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

Chapter: 6 Problem: 6.123

Chemistry 12
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 J/8C. This observation, now called Dulong and Petits law, was used to estimate the specific heat of metals. Verify the law for the

Chapter: 6 Problem: 6.124

Chemistry 12
Determine the standard enthalpy of formation of ethanol (C2H5OH) from its standard enthalpy of combustion (21367.4 kJ/mol).

Chapter: 6 Problem: 6.125

Chemistry 12
Acetylene (C2H2) and benzene (C6H6) have the same empirical formula. In fact, benzene can be made from acetylene as follows: 3C2H2(g) C6H6(l) The enthalpies of combustion for C2H2 and C6H6 are 21299.4 kJ/mol and 23267.4 kJ/mol, respectively. Calculate the standard enthalpies of formation of C2H2 and

Chapter: 6 Problem: 6.126

Chemistry 12
Ice at 08C is placed in a Styrofoam cup containing 361 g of a soft drink at 238C. 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 08C. Determine the mass of ice that has melted. Ignore the heat capaci

Chapter: 6 Problem: 6.127

Chemistry 12
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 everyones surprise, the candle was relighted. Explain how the host was able to accomplish the task without touching the

Chapter: 6 Problem: 6.128

Chemistry 12
How much heat is required to decompose 89.7 g of NH4Cl? (Hint: You may use the enthalpy of formation values at 258C for the calculation.)

Chapter: 6 Problem: 6.129

Chemistry 12
A gas company in Massachusetts charges $1.30 for 15 ft3 of natural gas (CH4) measured at 208C and 1.0 atm. Calculate the cost of heating 200 mL of water (enough to make a cup of coffee or tea) from 208C to 1008C. Assume that only 50 percent of the heat generated by the combustion is used to heat the

Chapter: 6 Problem: 6.13c

Chemistry 12
Calculate the internal energy of a Goodyear blimp filled with helium gas at 1.2 3 105 Pa. The volume of the blimp is 5.5 3 103 m3 . If all the energy were used to heat 10.0 tons of copper at 218C, calculate the final temperature of the metal. (Hint: See Section 5.7 for help in calculating the interna

Chapter: 6 Problem: 6.131

Chemistry 12
Decomposition reactions are usually endothermic, whereas combination reactions are usually exothermic. Give a qualitative explanation for these trends

Chapter: 6 Problem: 6.132

Chemistry 12
Acetylene (C2H2) can be made by reacting calcium carbide (CaC2) 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 g of CaC2?

Chapter: 6 Problem: 6.133

Chemistry 12
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

Chapter: 6 Problem: 6.134

Chemistry 12
When 1.034 g of naphthalene (C10H8) are burned in a constant-volume bomb calorimeter at 298 K, 41.56 kJ of heat are evolved. Calculate DU and DH for the reaction on a molar basis

Chapter: 6 Problem: 6.135

Chemistry 12
From a thermochemical point of view, explain why a carbon dioxide fire extinguisher or water should not be used on a magnesium fire.

Chapter: 6 Problem: 6.136

Chemistry 12
Calculate the DU for the following reaction at 298 K: 2H2(g) 1 O2(g) 2H2O(l)

Chapter: 6 Problem: 6.137

Chemistry 12
Lime is a term that includes calcium oxide (CaO, also called quicklime) and calcium hydroxide [Ca(OH)2, also called slaked lime]. It is used in the steel industry to remove acidic impurities, in airpollution control to remove acidic oxides such as SO2, and in water treatment. Quicklime is made indust

Chapter: 6 Problem: 6.138

Chemistry 12
A 4.117-g impure sample of glucose (C6H12O6) was burned in a constant-volume calorimeter having a heat capacity of 19.65 kJ/8C. If the rise in temperature is 3.1348C, calculate the percent by mass of the glucose in the sample. Assume that the impurities are unaffected by the combustion process. See A

Chapter: 6 Problem: 6.139

Chemistry 12
Construct a table with the headings q, w, DU, and DH. For each of the following processes, deduce whether each of the quantities listed is positive (1), negative (2), or zero (0). (a) Freezing of benzene. (b) Compression of an ideal gas at constant temperature. (c) Reaction of sodium with water. (d)

Chapter: 6 Problem: 6.14c

Chemistry 12
The combustion of 0.4196 g of a hydrocarbon releases 17.55 kJ of heat. The masses of the products are CO2 5 1.419 g and H2O 5 0.290 g. (a) What is the empirical formula of the compound? (b) If the approximate molar mass of the compound is 76 g, calculate its standard enthalpy of formation

Chapter: 6 Problem: 6.141

Chemistry 12
Metabolic activity in the human body releases approximately 1.0 3 104 kJ of heat per day. Assuming the body is 50 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 (98.68F

Chapter: 6 Problem: 6.142

Chemistry 12
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 systems temperature is changed even though no heat is added or removed from it.

Chapter: 6 Problem: 6.143

Chemistry 12
From the following data, calculate the heat of solution for KI: NaCl NaI KCl KI Lattice energy 788 686 699 632 (kJ/mol) Heat of solution 4.0 25.1 17.2 ?

Chapter: 6 Problem: 6.144

Chemistry 12
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? P (atm) 1 2 V (L) 2 1 B C A D

Chapter: 6 Problem: 6.145

Chemistry 12
For reactions in condensed phases (liquids and solids), the difference between DH and DU 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 DH and DU can differ by

Chapter: 6 Problem: 6.146

Chemistry 12
The diagrams shown here represent various physical and chemical processes. (a) 2A(g) A2(g). (b) MX(s) M1(aq) 1 X2(aq). (c) AB(g) 1 C(g) AC(g) 1 B(g). (d) B(l) B(g). Predict whether the situations shown are endothermic or exothermic. Explain why in some cases no clear conclusions can be made. (a)

Chapter: 6 Problem: 6.147

Chemistry 12
A 20.3-g sample of an unknown metal and a 28.5-g sample of copper, both at 80.68C, are added to 100 g of water at 11.28C in a constant-pressure calorimeter of negligible heat capacity. If the final temperature of the metals and water is 13.78C, determine the specific heat of the unknown metal.

Chapter: 6 Problem: 6.148

Chemistry 12
For most biological processes, DH < DU. Explain

Chapter: 6 Problem: 6.149

Chemistry 12
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.

Chapter: 6 Problem: 6.15c

Chemistry 12
The fastest serve in tennis is about 150 mph. Can the kinetic energy of a tennis ball traveling at this speed be sufficient to heat 1 mL of water by 308C?

Chapter: 6 Problem: 6.151

Chemistry 12
Can the total energy output of the sun in one second be sufficient to heat all of the ocean water on Earth to its boiling point?

Chapter: 6 Problem: 6.152

Chemistry 12
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 e

Chapter: 6 Problem: 6.153

Chemistry 12
Biomass plants generate electricity from waste material such as wood chips. Some of these plants convert the feedstock to ethanol (C2H5OH) 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 C2H5OH? (b) How muc

Chapter: 6 Problem: 6.154

Chemistry 12
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?

Chapter: 6 Problem: 6.155

Chemistry 12
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 its like paying $5 a gallon. But you go two to three times as far on the hydrogen

Chapter: 6 Problem: 6.156

Chemistry 12
We hear a lot about how the burning of hydrocarbons produces the greenhouse gas CO2, 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 energy world consumption. (a) How many moles of oxyge

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