Chapter 8 1 In which case is the work done on the system always positive

General Chemistry: Atoms First, 2e (McMurry and Fay)

Chapter 8 Thermochemistry: Chemical Energy

8.1 Multiple Choice Questions

1) At 298 K the average kinetic energy is the same for H2, He, and N2. The gas with the highest

average velocity is

A) H2.

B) He.

C) N2.

D) All have the same average velocity.

2) Which of the following is not a type of energy or energy transfer?

A) chemical energy

B) heat

C) pressure

D) work

3) Which of the following is not a state function?

A) altitude

B) heat

C) internal energy

D) volume

4) The first law of thermodynamics

A) defines chemical energy.

B) defines entropy.

C) is a statement of conservation of energy.

D) provides a criterion for the spontaneity of a reaction.

5) 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

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

A) ΔE > 0

B) ΔV > 0

C) ΔV = 0

D) ΔV < 0

7) Calculate the work energy, w, gained or lost by the system when a gas expands from 15 L to

35 L against a constant external pressure of 1.5 atm. [1 L ∙ atm = 101 J]

A) -5.3 kJ

B) -3.0 kJ

C) +3.0 kJ

D) +5.3 kJ

8) 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.

9) 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 = T¹S

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

A) q

B) w

C) q + w

D) q – w

11) 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.

12) For a process at constant pressure,

A) ΔE = w and q = 0.

B) ΔE = q and w = 0.

C) ΔE = ΔH.

D) ΔH = q.

13) 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

14) For a particular process that is carried out at constant pressure, q = 125 kJ and w = -15 kJ.

Therefore,

A) ΔE = 110 kJ and ΔH = 125 kJ.

B) ΔE = 125 kJ and ΔH = 110 kJ.

C) ΔE = 125 kJ and ΔH = 140 kJ.

D) ΔE = 140 kJ and ΔH = 125 kJ.

15) 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.

16) 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.

17) 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.

18) For the reaction shown below, at constant pressure what can be said about P△V and △E?

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

A) P△V > 0 and △E > – 92.2 kJ

B) P△V > 0 and △E < – 92.2 kJ

C) P△V < 0 and △E > – 92.2 kJ

D) P△V < 0 and △E < – 92.2 kJ

19) At constant pressure for which of the reactions shown below should ΔH° be greater than ΔE° ?

I. 2 SO2(g) + O2(g) → 2 SO3(g)

II. C3H8(g) + 5 O2(g) → 3 CO2(g) + 4 H2O(l)

III. H2(g) + Cl2(g) → 2 HCl(g)

IV. N2O4(g) → 2 NO2(g)

A) I.

B) III.

C) IV.

D) II. and IV.

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

A) O(g)

B) O2(g)

C) O2(l)

D) O3(g)

21) 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

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

boiling point of 80.1°C, 33.9 kJ are absorbed and PΔV for the vaporization process is equal to

2.90 kJ, then

A) ΔE = 31.0 kJ and ΔH = 33.9 kJ.

B) ΔE = 36.8 kJ and ΔH = 33.9 kJ.

C) ΔE = 33.9 kJ and ΔH = 31.0 kJ.

D) ΔE = 33.9 kJ and ΔH = 36.8 kJ.

23) 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.

24) When 2.000 moles of H2(g) reacts with 1.000 mol of O2(g) to form 2.000 mol of H2O(l) at

25°C and a constant pressure of 1.00 atm. If 136.6 kJ of heat are released during this reaction,

and PΔV is equal to -7.400 kJ, then

A) ΔH° = +136.6 kJ and ΔE° = +144.0 kJ.

B) ΔH° = +136.6 kJ and ΔE° = +129.2 kJ.

C) ΔH° = –136.6 kJ and ΔE° = -129.2 kJ.

D) ΔH° = –136.6 kJ and ΔE° = -144.0 kJ.

25) The enthalpy of fusion, or heat of fusion (△Hfusion), 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)

26) 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.

27) 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)

28) 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

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29) 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 1.50 mol of gallium at 1 atm

pressure?

A) 6 kJ

B) 9 kJ

C) 268 kJ

D) 271 kJ

30) How much heat is transferred per mole of NH3(g) formed in the reaction shown below?

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

A) 92.2 kJ

B) 46.1 kJ

C) 30.7 kJ

D) 15.4 kJ

31) How much heat is absorbed/released when 20.00 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) 342.9 kJ of heat are absorbed.

B) 342.9 kJ of heat are released.

C) 1372 kJ of heat are absorbed.

D) 1372 kJ of heat are released.

32) How much heat is absorbed when 30.00 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) 119.9 kJ

B) 239.9 kJ

C) 599.2 kJ

D) 1439 kJ

33) At constant pressure, the combustion of 5.00 g of C2H6(g) releases 259 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) -3108 kJ

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

that is absorbed/released when 5.00 g of steam condenses to liquid water at 100°C.

A) 11.3 kJ of heat are absorbed.

B) 11.3 kJ of heat are released.

C) 147 kJ of heat are absorbed.

D) 147 kJ of heat are released.

35) When 0.250 mol of CH4(g) reacts with excess Cl2(g) at constant pressure according to the

chemical equation shown below, 177 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) -1420 kJ

B) -708 kJ

C) +708 kJ

D) +1420 kJ

36) Calculate the total quantity of heat required to convert 25.0 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

its heat of fusion is and its heat of vaporization is

A) 1.11 kJ

B) 1.64 kJ

C) 5.96 kJ

D) 6.49 kJ

37) 10.0 g of a metal, initially at 25°C, are placed into 10.0 g of water, initially at 100°C. Which

metal will have the highest final temperature? Shown after each metal is its specific heat in

J/(g∙°C).

A) aluminum (0.902)

B) copper (0.385)

C) gold (0.129)

D) iron (0.450)

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

4.689 kJ, what will be the final temperature of the copper?

A) 25.4°C

B) 27.8°C

C) 356°C

D) 381°C

39) It takes 11.2 kJ of energy to raise the temperature of 145 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)

40) Water has an unusually high

A) electrical conductivity.

B) heat of combustion.

C) heat of formation.

D) specific heat.

41) When 1.50 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 33.10°C. If the specific heat of the solution is calculate 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

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

the chemical equation shown below. When 0.0300 mol of Na is added to 100.00 g of water, the

temperature of the resulting solution rises from 25.00°C to 37.90°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) -364 kJ

43) 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 25.00°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 calculate the final temperature of the

solution.

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

A) 24.45°C

B) 25.55°C

C) 26.10°C

D) 26.65°C

44) When 0.455 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 8.63°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) -7070 kJ/mol

D) -8120 kJ/mol

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45) 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

46) 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), and 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

47) Given: 4 NO2(g) + O2(g) → 2 N2O5(g) ΔH° = -110.2 kJ

find ΔH° for N2O5(g) → 2 NO2(g) + 1/2 O2(g).

A) -220.4 kJ

B) -55.1 kJ

C) 55.1 kJ

D) 220.4 kJ

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48) 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

49) Find ΔH for BaCO3 (s) → BaO (s)+ CO2 (g)

given 2 Ba (s) + O2 (g) → 2 BaO (s) ΔH = -1107.0 kJ

Ba (s) + CO2 (g) + 1/2 O2 (g) → BaCO3 (g) ΔH = -822.5 kJ

A) -1929.5 kJ

B) -1376.0 kJ

C) -284.5 kJ

D) 269.0 kJ

50) Find ΔH for C3H8 (g) + 6 H2O (g) → 3 CO2 (g) + 10 H2

given C3H8 (g) + 3 H2O (g) → 3 CO (g) + 7 H2 (g) ΔH = 499 kJ

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

A) 376 kJ

B) 458 kJ

C) 540 kJ

D) 622 kJ

51) For which should the standard heat of formation ΔH°f, be zero at 25°C?

A) O(g)

B) O2(g)

C) O3(g)

D) all the above

52) Which is expected to have the most negative standard enthalpy of formation?

A) H2(g)

B) O2(g)

C) H2O(g)

D) H2O(l)

53) 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

54) 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)

55) 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

56) 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

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57) Acetylene torches utilize the following reaction:

2 C2H2(g) + 5 O2(g) → 4 CO2(g) + 2 H2O(g)

Use the given standard enthalpies of formation to calculate ΔH° for this reaction

A) 2512.4 kJ

B) 1256.2 kJ

C) -1256.2 kJ

D) -2512.4 kJ

58) 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

59) 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

60) 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

61) Use the given average bond dissociation energies, D, to estimate ΔH for the following

reaction:

C I(g) + (g) →C (g) + HI(g)

A) -32 kJ

B) +32 kJ

C) 378 kJ

D) -378 kJ

62) Use the given average bond dissociation energies, D, to estimate ΔH for the following

reaction:

C Br(g) + (g) →C (g) + HBr(g)

A) -70 kJ

B) +70 kJ

C) 340 kJ

D) -340 kJ

63) Use the given average bond dissociation energies, D, to estimate ΔH for the following

reaction:

C F(g) + (g) →C (g) + HF(g)

A) -94 kJ

B) +94 kJ

C) 316 kJ

D) -316 kJ

64) Use the given average bond dissociation energies, D, to estimate ΔH for the following

reaction:

C Cl(g) + (g) →C (g) + HCl(g)

A) -76 kJ

B) +76 kJ

C) 334 kJ

D) -334 kJ