Thermodynamics Examples of Multiple Choice Questions

1.

Which one of the following thermodynamic quantities is not a state function?

(a) Gibbs free energy

(b) enthalpy

(c) entropy

(d) internal energy

(e) work

2.

At a constant temperature, an ideal gas is compressed from 6.0 liters to 4.0 liters by a constant external pressure of 5.0 atm. How much work is done on the gas?

(a) w = +10 liter atm

(b) w = -10 liter atm

(c) w = +30 liter atm

(d) w = -30 liter atm

(e) The answer cannot be calculated.

3.

A system suffers an increase in internal energy of 80 J and at the same time has 50 J of work done on it. What is the heat change of the system?

(a) +130 J

(b) +30 J

(c) -130 J

(d) -30 J

(e) 0 J

4.

A 5.000 g sample of methanol, CH₃OH, was combusted in the presence of excess oxygen in a bomb calorimeter conaining 4000 g of water. The temperature of the water increased from 24.000 ^oC to 29.765 ^oC. The heat capacity of the calorimeter was 2657 J/^oC. The specific heat of water is 4.184 J/g^oC. Calculate E for the reaction in kJ/mol.

(a) -314 kJ/mol

(b) -789 kJ/mol

(c) -716 kJ/mol

(d) -121 kJ/mol

(e) -69.5 kJ/mol

5.

A coffee cup calorimeter having a heat capacity of 451 J/^oC was used to measure the heat evolved when 0.0300 mol of NaOH(s) was added to 1000 mL of 0.0300 M HNO₃ initially at 23.000 ^oC. The temperature of the water rose to 23.639 ^oC. Calculate H (in kJ/mol NaNO₃) for this reaction. Assume the specific heat of the final solution is 4.18 J/g^oC; the density of each solution is 1.00 g/mL; and the addition of solid does not appreciably affect the volume of the solution. HNO₃(aq) + NaOH(s) NaNO₃(aq) + H₂O(l)

(a) -63.7 kJ/mol

(b) -151 kJ/mol

(c) -2.55 kJ/mol

(d) -81.4 kJ/mol

(e) -98.6 kJ/mol

6.

The H^o for the following reaction at 298 K is -36.4 kJ. 1/2 H₂(g) + 1/2 Br₂(l) HBr(g) Calculate E^o at 298 K. The universal gas constant, R, is 8.314 J/mol K.

(a) -35.2 kJ

(b) +35.2 kJ

(c) -36.4 kJ

(d) -37.6 kJ

(e) +37.6 kJ

7.

Calculate the amount of work done for the conversion of 1.00 mole of Ni to Ni(CO)₄ in the reaction below, at 75^oC. Assume that the gases are ideal. The value of R is 8.31 J/molK. Ni(s) + 4 CO (g) Ni(CO)₄(g)

(a) 1.80 x 10³ J

(b) 8.68 x 10³ J

(c) -1.80 x 10³ J

(d) -8.68 x 10³ J

(e) -494 J

8.

All of the following have a standard heat of formation value of zero at 25^oC and 1.0 atm except:

(a) N₂(g)

(b) Fe(s)

(c) Ne(g)

(d) H(g)

(e) Hg(l)

9.

For which of the following reactions would the H^o for the reaction be labeled H_f^o?

(a) Al(s) + 3/2 H₂(g) + 3/2 O₂(g) Al(OH)₃(s)

(b) PCl₃(g) + 1/2 O₂(g) POCl₃(g)

(c) 1/2 N₂O(g) + 1/4 O₂(g) NO(g)

(d) CaO(s) + SO₂(g) CaSO₃(s)

(e) The H^o for all these reactions would be labeled H_f^o.

10.

Calculate H^o for the reaction: Na₂O(s) + SO₃(g) Na₂SO₄(g) given the following information:

	Ho
(1) Na(s) + H2O(l) NaOH(s) + 1/2 H2(g)	-146 kJ
(2) Na2SO4(s) + H2O(l) 2NaOH(s) + SO3(g)	+418 kJ
(3) 2Na2O(s) + 2H2(g) 4Na(s) + 2H2O(l)	+259 kJ

(a) +255 kJ

(b) -435 kJ

(c) -581 kJ

(d) +531 kJ

(e) -452 kJ

11.

Calculate H^o_rxn for the following reaction at 25.0 ^oC:

	Fe3O4(s)	+	CO(g)		3FeO(s)	+	CO2(g)
Hfo (kJ/mol)	-1118		-110.5		-272		-393.5

(a) -263 kJ

(b) 54 kJ

(c) 19 kJ

(d) -50 kJ

(e) 109 kJ

12.

Calculate the standard heat of formation, H_f^o, for FeS₂(s), given the following information: 2FeS₂(s) + 5O₂(g) 2FeO(s) + 4SO₂(g)

H^o_rxn = -1370 kJ

H_f^o for SO₂(g) = -297 kJ/mol

H_f^o for FeO(s) = -268 kJ/mol

(a) -177 kJ

(b) -1550 kJ

(c) -774 kJ

(d) -686 kJ

(e) +808 kJ

13.

Estimate the heat of reaction at 298 K for the reaction shown, given the average bond energies below. Br₂(g) + 3F₂(g) 2BrF₃(g)

Bond		Bond Energy
Br-Br		192 kJ
F-F		158 kJ
Br-F		197 kJ

(a) -516 kJ

(b) -410 kJ

(c) -611 kJ

(d) -665 kJ

(e) -720 kJ

14.

What is the standard entropy change of the reaction below at 298 K with each compound at the standard pressure?

	N2(g)	+	3H2(g)		2NH3(g)
So298 (J/mol K)	191.5		130.6		192.3

(a) -198.7 J/K

(b) 76.32 J/K

(c) 303.2 J/K

(d) -129.7 J/K

(e) 384.7 J/K

15.

The entropy will usually increase when

I. a molecule is broken into two or more smaller molecules.

II. a reaction occurs that results in an increase in the number of moles of gas.

III. a solid changes to a liquid.

IV. a liquid changes to a gas.

(a) I only

(b) II only

(c) III only

(d) IV only

(e) I, II, III, and IV

16.

Calculate G^o for the reaction given the following information: 2SO₂(g) + O₂(g) 2SO₃(g)

G_f^o for SO₂(g) = -300.4 kJ/mol

G_f^o for SO₃(g) = -370.4 kJ/mol

(a) -70.0 kJ

(b) +70.0 kJ

(c) -670.8 kJ

(d) -140.0 kJ

(e) +140.0 kJ

17.

For the following reaction at 25^oC, H^o = +115 kJ and S^o = +125 J/K. Calculate G^o for the reaction at 25^o. SBr₄(g) S(g) + 2Br₂(l)

(a) +152 kJ

(b) -56.7 kJ

(c) +77.8 kJ

(d) +37.1 kJ

(e) -86.2 kJ

18.

The heat of vaporization of freon, CCl₂F₂, is 17.2 kJ/mol at 25^oC. What is the change of entropy for one mole of liquid freon when it vaporizes at 25^oC? (Hint: The vaporization process is at equilibrium and what is true for G at equilibrium?)

(a) 57.7 J/K

(b) 0.688 J/K

(c) 5.13 x 10³ kJ/K

(d) 3.16 J/K

(e) 239 J/K

19.

Estimate the boiling point of Br₂(l) (H = 30.9 kJ; S = 93.0 J/K). Br₂(l) Br₂(g)

(a) 85^oC

(b) 373^oC

(c) 177^oC

(d) 59^oC

(e) 44^oC

20.

For the reaction, A + B C, H^o = +30 kJ; S^o = +50 J/K.
Therefore the reaction is:

(a) spontaneous at all temperatures.

(b) nonspontaneous at all temperatures.

(c) spontaneous at temperatures less than 600 K.

(d) spontaneous at temperatures greater than 600 K.

(e) spontaneous only at 25^oC.

21.

How much heat is absorbed in the complete reaction of 3.00 grams of SiO₂ with excess carbon in the reaction below? H^o for the reaction is +624.7 kJ. SiO₂(s) + 3C(s) SiC(s) + 2CO(g)

(a) 366 kJ

(b) 1.13 x 10⁵ kJ

(c) 5.06 kJ

(d) 1.33 x 10⁴ kJ

(e) 31.2 kJ

22.

The standard heat of combustion of ethanol, C₂H₅OH, is 1372 kJ/mol ethanol. How much heat (in kJ) would be liberated by completely burning a 20.0 g sample?

(a) 686 kJ

(b) 519 kJ

(c) 715 kJ

(d) 597 kJ

(e) 469 kJ

23.

Which statement is incorrect?

(a) At constant pressure, H = E + PV

(b) The thermodynamic symbol for entropy is S.

(c) Gibbs free energy is a state function.

(d) For an endothermic process, H is negative.

(e) If the work done by the system is greater than the heat absorbed by the system, E is negative.

24.

Which statement is false?

(a) The thermodynamic quantity most easily measured in a "coffee cup" calorimeter is H.

(b) No work is done in a reaction occurring in a bomb calorimeter.

(c) H is sometimes exactly equal to E.

(d) H is often nearly equal to E.

(e) H is equal to E for the reaction: 2H₂(g) + O₂(g) 2H₂O(g)

Answers:

1. (e) 2. (a) 3. (b) 4. (c) 5. (e) 6. (d) 7. (b) 8. (d) 9. (a) 10. (c) 11. (c) 12. (a) 13. (a) 14. (a) 15. (e) 16. (d) 17. (c) 18. (a) 19. (d) 20. (d) 21. (e) 22. (d) 23. (d) 24. (e)

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