Chapter 9 1 Which is a measure of the sum of the kinetic and potential

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Chemistry, 7e (McMurry/Fay)

Chapter 9 Thermochemistry: Chemical Energy

9.1 Multiple-Choice Questions

1) Which of the following states the first law of thermodynamics (conservation of energy)?

A) w = –PΔV

B) ΔEsystem = –ΔEsurroundings

C) ΔH = ΔE + PΔV

D) q = smΔT

2) Which is a measure of the sum of the kinetic and potential energies of each particle in the system?

A) E, the internal energy

B) G, the Gibbs free energy

C) H, the enthalpy

D) T, the temperature

3) In which case is the work done on the system always positive?

A) ΔE > 0

B) ΔV > 0

C) ΔV = 0

D) ΔV < 0

4) Calculate the work energy, w, gained or lost by the system when a gas expands from 20 L to 35 L

against a constant external pressure of 2.0 atm. [1 L ∙ atm = 101 J]

A) -5.3 kJ

B) -3.0 kJ

C) +3.0 kJ

D) +5.3 kJ

5) What is expected when the reaction shown below takes place in a thermally–insulated container

outfitted with a movable piston at a constant atmospheric pressure of 1 atm?

2 C2H6(g) + 7 O2(g) → 4 CO2(g) + 6 H2O(g)

A) Volume will decrease and work will be done by the system.

B) Volume will decrease and work will be done on the system.

C) Volume will increase and work will be done by the system.

D) Volume will increase and work will be done on the system.

6) An ideal gas expands into a vacuum (external pressure = 0) without gaining or losing heat. For this

expansion

A) ΔE increases.

B) ΔE does not change.

C) ΔE decreases.

D) ΔE = TΔS.

7) Which depends only on the initial and final state?

A) q

B) w

C) q + w

D) q – w

8) For a process at constant volume,

A) q = 0, w = 0, and ΔE = 0.

B) w = 0 and ΔE = q.

C) w = 0 and ΔH = q.

D) w = 0 and ΔE = ΔH.

9) For a process at constant pressure,

A) ΔE = w and q = 0.

B) ΔE = q and w = 0.

C) ΔE = ΔH.

D) ΔH = q.

10) Most chemical reactions are carried out in one of two ways:

I. in an open vessel at constant atmospheric pressure

II. in a closed vessel

Which is true?

A) ΔH = q for condition I and ΔE = q for condition II.

B) ΔE = q for condition I and ΔH = q for condition II.

C) ΔH = w for condition I and ΔE = w for condition II.

D) ΔE = w for condition I and ΔH = w for condition II.

11) For a particular process that is carried out at constant pressure, q = 200 kJ and w = -85 kJ. Therefore,

A) ΔE = 115 kJ and ΔH = 200 kJ.

B) ΔE = 200 kJ and ΔH = 115 kJ.

C) ΔE = 200 kJ and ΔH = 285 kJ.

D) ΔE = 285 kJ and ΔH = 200 kJ.

12) For most chemical reactions

A) ΔH is much larger than ΔE.

B) ΔE is much larger than ΔH.

C) ΔH is equal to ΔE.

D) the difference between ΔH and ΔE is very small.

13) A process is carried out at constant pressure. Given that ΔE is positive and ΔH is negative,

A) the system absorbs heat and expands during the process.

B) the system absorbs heat and contracts during the process.

C) the system loses heat and expands during the process.

D) the system loses heat and contracts during the process.

14) A process is carried out at constant pressure. Given that 0 > ΔH > ΔE,

A) the system absorbs heat and expands during the process.

B) the system absorbs heat and contracts during the process.

C) the system loses heat and expands during the process.

D) the system loses heat and contracts during the process.

15) At constant pressure for the reaction shown below, what can be said about PΔV and ΔE?

N2(g) + 3 H2(g) → 2 NH3(g) ΔH° = – 92.2 kJ

A) PΔV > 0 and ΔE > -92.2 kJ

B) PΔV > 0 and ΔE < -92.2 kJ

C) PΔV < 0 and ΔE > -92.2 kJ

D) PΔV < 0 and ΔE < -92.2 kJ

16) Under thermodynamic standard state conditions the element oxygen occurs as

A) O(g)

B) O2(g)

C) O2(l)

D) O3(g)

17) Find ΔE° for the reaction below if the process is carried out at a constant pressure of 1.00 atm and ΔV

(the volume change) = –24.5 L. (1 L ∙ atm = 101 J)

2 CO(g) + O2 (g) → 2 CO2(g) ΔH° = -566. kJ

A) +2.47 kJ

B) -2.47 kJ

C) -564 kJ

D) -568 kJ

18) When 10.0 mol of benzene is vaporized at a constant pressure of 1.00 atm and at its normal boiling

point of 80.1°C, 339 kJ are absorbed and PΔV for the vaporization process is equal to 29.0 kJ, then

A) ΔE = 310. kJ and ΔH = 339. kJ.

B) ΔE = 368. kJ and ΔH = 339. kJ.

C) ΔE = 339. kJ and ΔH = 310. kJ.

D) ΔE = 339. kJ and ΔH = 368. kJ.

19) For an explosion in an open vessel, one would expect

A) ΔH to be positive and ΔE to be less than ΔH.

B) ΔH to be positive and ΔE to be greater than ΔH.

C) ΔH to be negative and ΔE to be less than ΔH.

D) ΔH to be negative and ΔE to be greater than ΔH.

20) When 20.00 moles of H2(g) reacts with 10.00 mol of O2(g) to form 20.00 mol of H2O(l) at 25°C and a

constant pressure of 1.00 atm. If 1366 kJ of heat are released during this reaction, and PΔV is equal to –

74.00 kJ, then

A) ΔH° = +1366 kJ and ΔE° = +1440 kJ.

B) ΔH° = +1366 kJ and ΔE° = +1292 kJ.

C) ΔH° = –1366 kJ and ΔE° = –1292 kJ.

D) ΔH° = –1366 kJ and ΔE° = -1440 kJ.

21) Which of the following scenarios involves a transfer of heat from system to surroundings?

A) evaporating rubbing alcohol from your skin

B) solidifying molten gold into a gold bar

C) melting solid gallium metal with heat from your hand

D) none of these

22) The enthalpy of fusion, or heat of fusion (ΔHfusion), of water is positive and corresponds to which

physical change?

A) H2O(g) → H2O(s)

B) H2O(l) → H2O(s)

C) H2O(s) → H2O(l)

D) H2O(s) → H2O(g)

23) For the reaction I2(g) → I2(s), ΔH° = -62.4 kJ at 25°C. Based on these data, at 25°C

A) ΔH°vap = -62.4 kJ/mol.

B) ΔH°vap = 62.4 kJ/mol.

C) ΔH°sub = -62.4 kJ/mol.

D) ΔH°sub = 62.4 kJ/mol.

24) Which is the most exothermic reaction?

A) CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(g)

B) CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(l)

C) CO2(g) + 2 H2O(l) →CH4(g) + 2 O2(g)

D) CO2(g) + 2 H2O(g) →CH4(g) + 2 O2(g)

25) At 25°C the heat of fusion of aluminum is 10.6 kJ/mol and the heat of sublimation is 326.4 kJ/mol.

What is the heat of vaporization of aluminum at 25°C?

A) 158.2 kJ/mol

B) 168.5 kJ/mol

C) 315.8 kJ/mol

D) 337.0 kJ/mol

26) At 1 atm pressure the heat of sublimation of gallium is 277 kJ/mol and the heat of vaporization is 271

kJ/mol. How much heat is required to melt 0.500 mol of gallium at 1.00 atm pressure?

A) 6.00 kJ

B) 3.00 kJ

C) 268 kJ

D) 271 kJ

27) How much heat is absorbed/released when 10.00 g of NH3(g) reacts in the presence of excess O2(g) to

produce NO(g) and H2O(l) according to the following chemical equation?

4 NH3(g) + 5 O2(g) → 4 NO(g) + 6 H2O(l) ΔH° = +1168 kJ

A) 171.5 kJ of heat are absorbed.

B) 171.5 kJ of heat are released.

C) 686.0 kJ of heat are absorbed.

D) 686.0 kJ of heat are released.

28) How much heat is absorbed when 20.00 g of C(s) reacts in the presence of excess SO2(g) to produce

CS2(l) and CO(g) according to the following chemical equation?

5 C(s) + 2 SO2(g) → CS2(l) + 4 CO(g) ΔH° = +239.9 kJ

A) 79.97 kJ

B) 159.9 kJ

C) 399.5 kJ

D) 959.3 kJ

29) At constant pressure, the combustion of 30.00 g of C2H6(g) releases 1560 kJ of heat. What is ΔH for the

reaction given below?

2 C2H6(g) + 7 O2(g) → 4 CO2(g) + 6 H2O(l)

A) -43.2 kJ

B) -779 kJ

C) -1560 kJ

D) -3120 kJ

30) The heat of vaporization of water at 100°C is 40.66 kJ/mol. Calculate the quantity of heat that is

absorbed/released when 20.00 g of steam condenses to liquid water at 100°C.

A) 45.2 kJ of heat are absorbed.

B) 45.2 kJ of heat are released.

C) 813.2 kJ of heat are absorbed.

D) 813.2 kJ of heat are released.

31) When 2.500 mol of CH4(g) reacts with excess Cl2(g) at constant pressure according to the chemical

equation shown below, 1770. kJ of heat are released. Calculate the value of ΔH for this reaction, as

written.

2 CH4(g) + 3 Cl2(g) → 2 CHCl3(l) + 3 H2(g) ΔH = ?

A) -1416 kJ

B) -708.0 kJ

C) +708.0 kJ

D) +1416 kJ

32) Calculate the total quantity of heat required to convert 50.0 g of liquid CCl4(l) from 25.0°C to gaseous

CCl4 at 76.8°C (the normal boiling point for CCl4)? The specific heat of CCl4(l) is 0.857 J/(g ∙ °C), its heat

of fusion is and its heat of vaporization is

A) 2.22 kJ

B) 3.28 kJ

C) 11.91 kJ

D) 12.98 kJ

33) In the lab, you mix two solutions (each originally at the same temperature) and the temperature of the

resulting solution decreases. Which of the following is true?

A) The chemical reaction is releasing energy.

B) The energy released is equal to s × m × ΔT.

C) The chemical reaction is absorbing energy.

D) The chemical reaction is exothermic.

34) The specific heat of copper is 0.385 J/(g ∙ °C). If 34.2 g of copper, initially at 25°C, absorbs 7.880 kJ,

what will be the final temperature of the copper?

A) 25.4°C

B) 27.8°C

C) 598°C

D) 623°C

35) It takes 15.5 kJ of energy to raise the temperature of 200 g of benzene from 25.0°C to 70.0°C. What is

the specific heat of benzene?

A) 1.10 J/(g ∙ °C)

B) 1.72 J/(g ∙ °C)

C) 3.48 J/(g ∙ °C)

D) 5.41 J/(g ∙ °C)

36) Water has an unusually high

A) electrical conductivity.

B) heat of combustion.

C) heat of formation.

D) specific heat.

37) When 8.00 g of Ba(s) is added to 100.00 g of water in a container open to the atmosphere, the reaction

shown below occurs and the temperature of the resulting solution rises from 22.00°C to 77.62°C. If the

specific heat of the solution is 4.18 J/(g ∙ °C), calculate ΔH for the reaction, as written.

Ba(s) + 2 H2O(l) → Ba(OH)2(aq) + H2(g) ΔH = ?

A) -431 kJ

B) -3.14 kJ

C) 3.14 kJ

D) 431 kJ

38) Sodium metal reacts with water to produce hydrogen gas and sodium hydroxide according to the

chemical equation shown below. When 0.0500 mol of Na is added to 100.00 g of water, the temperature of

the resulting solution rises from 25.00°C to 46.23°C. If the specific heat of the solution is 4.18 J/(g ∙ °C),

calculate ΔH for the reaction, as written.

2 Na(s) + 2 H2O(l) → 2 NaOH(aq) + H2(g) ΔH = ?

A) -5.41 kJ

B) -90. 0 kJ

C) -180 kJ

D) -362 kJ

39) When 50.0 mL of 0.400 M Ca(NO3)2 is added to 50.0 mL of 0.800 M NaF, CaF2 precipitates, as shown

in the net ionic equation below. The initial temperature of both solutions is 30.00°C. Assuming that the

reaction goes to completion, and that the resulting solution has a mass of 100.00 g and a specific heat of

4.18 J/(g ∙ °C), calculate the final temperature of the solution.

Ca2+(aq) + 2 F–(aq) → CaF2(s) ΔH° = -11.5 kJ

A) 29.45°C

B) 30.55°C

C) 31.10°C

D) 31.65°C

40) When 0.700 g of anthracene, C14H10, is combusted in a bomb calorimeter that has a water jacket

containing 500. g of water, the temperature of the water increases by 13.27°C. Assuming that the specific

heat of water is 4.18 J/(g ∙ °C), and that the heat absorption by the calorimeter is negligible, estimate the

enthalpy of combustion per mole of anthracene.

A) +39.7 kJ/mol

B) -39.7 kJ/mol

C) -7060 kJ/mol

D) -8120 kJ/mol

41) Two metals of equal mass with different heat capacities are subjected to the same amount of heat.

Which undergoes the smallest change in temperature?

A) The metal with the highest heat capacity.

B) The metal with the lowest heat capacity.

C) Both undergo the same change in temperature.

D) You need to know the initial temperatures of both metals.

42) Given: S (s) + O2 (g) → SO2 (g) ΔH° = -296.1 kJ

2 SO3 (g) → 2 SO2 (g) + O2 (g) ΔH° = 198.2 kJ

Find ΔH° for : 2 S(s) + 3 O2(g) → 2 SO3(g)

A) -790.4 kJ

B) -394.0 kJ

C) -97.9 kJ

D) +97.9 kJ

43) Find ΔH° for the reaction C3H8(g) + 5 O2(g) → 3 CO2(g) + 4 H2O(l).

ΔH° = -2046 kJ for the reaction: C3H8(g) + 5 O2(g) → 3 CO2(g) + 4 H2O(g)

The heat of vaporization of water is 44.0 kJ/mol. Note that H2O is a liquid in the first reaction and a gas in

the second.

A) -2222 kJ

B) -2090 kJ

C) -2002 kJ

D) -1870 kJ

44) Coal gasification can be represented by the equation:

2 C(s) + 2 H2O(g) → CH4(g) + CO2(g) ΔH = ?

Use the following information to find ΔH for the reaction above.

CO(g) + H2(g) → C(s) + H2O(g) ΔH = -131 kJ

CO(g) + H2O(g) → CO2(g) + H2(g) ΔH = -41 kJ

CO(g) + 3 H2(g) → CH4(g) + H2O(g) ΔH = -206 kJ

A) 15 kJ

B) 116 kJ

C) -116 kJ

D) -372 kJ

45) The values of ΔH°f for the three states of benzene are approximately -22 kcal/mol, -11 kcal/mol, and

Which is the value for solid benzene?

A) -22 kcal/mol

B) -11 kcal/mol

C) 20 kcal/mol

D) cannot be determined without additional information

46) Which equation represents the reaction whose ΔH, represents the standard enthalpy of formation of

CHCl3(l) at 25°C? (i.e., for which is ΔH = ΔH°f of CHCl3)

A) CHCl3(l) → C(s) + H(g) + 3 Cl(g)

B) C(s) + H(g) + 3 Cl(g) → CHCl3(l)

C) C(s) + 1/2 H2(g) + 3/2 Cl2(g) → CHCl3(l)

D) 2 C(s) + H2(g) + 3 Cl2(g) → 2 CHCl3(l)

47) Use the given standard enthalpies of formation to calculate ΔH° for the following reaction

3 Fe2O3(s) + CO(g) → 2 Fe3O4(s) + CO2(g).

A) -5213.4 kJ

B) -577.2 kJ

C) -47.2 kJ

D) +47.2 kJ

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48) Ethyl alcohol is produced by the fermentation of glucose, C6H12O6.

C6H12O6(s) → 2 C2H5OH(l) + 2 CO2(g) ΔH° = -69.1 kJ

Given that the enthalpy of formation is -277.7 kJ/mol for C2H5OH(l) and -393.5 kJ/mol for CO2(g), find

the enthalpy of formation for C6H12O6.

A) -1411.5 kJ/mol

B) -1273.3 kJ/mol

C) -740.3 kJ/mol

D) -602.1 kJ/mol

49) For the reaction 2CH4 (g) + 3 Cl2 (g) → 2 CHCl3 (l) + 3 H2 (g), ΔH° = -118.6 kJ.

ΔH°f = -134.1 kJ/mol for CHCl3 (l). Find ΔH°f for CH4 (g).

A) -193.4 kJ/mol

B) -74.8 kJ/mol

C) 74.8 kJ/mol

D) 193.4 kJ/mol

50) One method for making ethanol, C2H5OH, involves the gas-phase hydration of ethylene, C2H4:

Estimate ΔH for this reaction from the given average bond dissociation energies, D.

A) –580 kJ

B) -35 kJ

C) +35 kJ

D) 580 kJ

51) Use the given average bond dissociation energies, D, to estimate ΔH for the reaction of methane,

CH4(g), with fluorine according to the equation:

CH4(g) + 2 F2(g) → CF4(g) + 2 H2(g)

A) -716 kJ

B) -318 kJ

C) +318 kJ

D) +716 kJ

52) Given that ΔH°= –311 kJ for the hydrogenation of acetylene, C2H2:

H—CC—H(g) + 2 H2(g) → CH3–CH3(g)

and the following bond dissociation energies, estimate a value for the C—to—C triple bond dissociation

energy.

A) 1050 kJ/mol

B) 833 kJ/mol

C) 807 kJ/mol

D) 397 kJ/mol

53) Heat of formation for CO is -110.5 KJ/mol and the heat of formation for MgO is -602 KJ/mol. Which of

the following statements is true?

A) The bond in CO is stronger than the bond in MgO.

B) The bond in MgO is stronger than the bond in CO.

C) The bonds in MgO and CO are equally strong.

D) Impossible to determine to given data.

54) Calculate the enthalpy of combustion per mole for C6H12O6. Assume that the combustion products

are CO2(g) and H2O(l).

A) -5336 kJ/mol

B) -2816 kJ/mol

C) -1939 kJ/mol

D) 580.7 kJ/mol

55) The heat of combustion per mole for acetylene, C2H2(g), is -1299.5 kJ/mol. Assuming that the

combustion products are CO2(g) and H2O(l), and given that the enthalpy of formation is -393.5 kJ/mol for

CO2(g) and -285.8 kJ/mol for H2O(l), find the enthalpy of formation of C2H2(g).

A) -846.1 kJ/mol

B) -620.2 kJ/mol

C) -226.7 kJ/mol

D) +226.7 kJ/mol

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56) Which of CH4(g), C2H2(g), and CH3OH(l) provides the most energy per gram upon combustion and

which provides the least?

CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(l) ΔH° = –890 kJ

2 C2H2(g) + 5 O2(g) → 4 CO2(g) + 2 H2O(l) ΔH° = -2599 kJ

2 CH3OH(l) + 3 O2(g) → 2 CO2(g) + 4 H2O(l) ΔH° = -1453 kJ

A) C2H2 provides the most energy per gram and CH4 the least.

B) C2H2 provides the most energy per gram and CH3OH the least.

C) CH4 provides the most energy per gram and CH3OH the least.

D) CH4 provides the most energy per gram and C2H2 the least.

57) Which of the following can be interpreted as a measure of randomness?

A) enthalpy

B) entropy

C) free energy

D) temperature

58) For the reaction, C2H2(g) → 2 C(g) + 2 H(g), one would expect

A) ΔH° to be negative and ΔS° to be negative.

B) ΔH° to be negative and ΔS° to be positive.

C) ΔH° to be positive and ΔS° to be negative.

D) ΔH° to be positive and ΔS° to be positive.

59) Determine the sign of ΔS° for each of the following:

I. C6H6(s) → C6H6(l)

II. 2 SO2(g) + O2(g) → 2 SO3(g)

A) ΔS° should be negative for I and negative for II.

B) ΔS° should be negative for I and positive for II.

C) ΔS° should be positive for I and negative for II.

D) ΔS° should be positive for I and positive for II.

60) Which thermodynamic function is most related to disorder and probability?

A) enthalpy

B) internal energy

C) entropy

D) heat capacity

61) For the expansion of an ideal gas into a vacuum at constant temperature, ΔH = 0. What can be said

about ΔE and ΔS?

A) ΔE is negative and ΔS is positive.

B) ΔE is zero and ΔS is positive.

C) ΔE is negative and ΔS is zero.

D) ΔE is positive and ΔS is negative.

62) For the of freezing liquid butane at a given temperature and pressure,

A) ΔH is negative and ΔS is negative.

B) ΔH is negative and ΔS is positive.

C) ΔH is positive and ΔS is negative.

D) ΔH is positive and ΔS is positive.