Unit 4 Practice Test: Thermochemistsry (Ch. 6 & 16)

1. The heat combustion of acetylene, C2H2(g), at 25°C, is -1299 kJ/mol. At this temperature, DHvalues for CO2(g) and H2O(l) are -393 and -286 kJ/mol, respectively. Calculate for acetylene.
[A] 2376 kJ/mol
[B] 227 kJ/mol
[C] -625 kJ/mol
[D] 625 kJ/mol
[E] none of these
2. Consider the following numbered processes:

DH for the process A ® 2C + E is

[A] DH1 + 2DH2 - DH3
[B] DH1 + DH2 - DH3
[C] DH1 + DH2 + DH3
[D] DH1 + 2DH2 + DH3
[E] DH1 + DH2
3. Which of the following statements correctly describes the signs of q and w for the following exothermic process at P = 1 atm and T = 370 K?
	H2O(g) ® H2O(l)
[A] q is positive, w is negative.
[B] q and w are both zero.
[C] q and w are negative.
[D] q and w are both positive.
[E] q is negative, w is positive.
4. A gas absorbs 0.0 J of heat and then performs 15.2 J of work. The change in internal energy of the gas is
[A] -24.8 J
[B] -15.2 J
[C] 14.8 J
[D] 55.2 J
[E] none of these
5. What is the heat capacity of mercury if it requires 167 J to change the temperature of 15.0 g mercury from 25.0°C to 33.0°C?
[A] 313 J/g°C
[B] 0.445 J/g°C
[C] 1.12 ´ 10-2 J/g°C
[D] 6.92 ´ 10-3 J/g°C
[E] 1.39 J/g°C
6. Consider a rigid insulated box containing 20.0 g of He(g) at 25.0°C and 1.00 atm in one compartment and 20.0 g of N2(g) at 115.0°C and 2.00 atm in the other compartment.  These compartments are connected by a partition which transmits heat.  What will be the final temperature in the box at thermal equilibrium? (CV(He) = 12.5 J/K mol, CV(N2) = 20.7 J/K mol)
[A] 58.9°C
[B] 81.0°C
[C] 42.2°C
[D] 70.0°C
[E] none of these
7. 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 chemical reaction is exothermic.
[C] The chemical reaction is absorbing energy.
[D] The energy released is equal to s ´ m ´ T.
[E] More than one of these.

8. Calculate the work associated with the compression of a gas from 121 L to 80. L at a constant pressure of 11 atm.

[A] 120 L × atm
[B] 3.7 L × atm
[C] -450 L × atm
[D] -3.7 L × atm
[E] 450 L × atm

9. 
Calculate the standard enthalpy of formation of CuO(s).
[A] +299 kJ
[B] -155 kJ
[C] +155 kJ
[D] -299 kJ
[E] -166 kJ
10. At 25°C, the following heats of reaction are known:
	
At the same temperature, calculate DH for the reaction:
	ClF + F2 ® ClF3
[A] -130.2 kJ/mol
[B] -217.5 kJ/mol
[C] -108.7 kJ/mol
[D] +217.5 kJ/mol
[E] none of these
11. The change in enthalpy can always be thought of as equal to energy flow as heat.
[A] True
[B] False
12. The heat of formation of Fe2O3(s) is -826 kJ/mol. Calculate the heat of the reaction 4Fe(s) + 3O2(g) ® 2Fe2O3(s) when a 55.8-g sample of iron is reacted.
[A] -413 kJ
[B] -3.30 ´ 103 kJ
[C] -206 kJ
[D] -826 kJ
[E] -1650 kJ
13. Consider the following reaction:
	2Al(s) + 3Cl2(g) ® 2AlCl3(s);    DH = -1390.81 kJ
a) Is the reaction exothermic or endothermic?
b) Calculate the heat produced when 10.0 g AlCl3 forms.
c) How many grams of Al are required to produce 1.00 kJ of energy?
14. Which of the following does not have a standard enthalpy of formation equal to zero at 25°C and 1.0 atm?
[A] F2(g)
[B] Al(s)
[C] H2(g)
[D] They all have a standard enthalpy equal to zero.
[E] H2O(l)
15. 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] Both undergo the same change in temperature.
[B] The metal with the higher heat capacity.
[C] The metal with the lower heat capacity.
[D] You need to know which metals you have.
[E] You need to know the initial temperatures of the metals.
16. Would you predict an increase or decrease in entropy for each of the following?
 2H2(g) + O2(g) ® 2H2O(g) 
17. Elemental sulfur exists in two crystalline forms, rhombic and monoclinic. From the following data, calculate the equilibrium temperature at which monoclinic sulfur and rhombic sulfur are in equilibrium.

[A] -210 K
[B] -450 K
[C] +210 K
[D] +450 K
[E] 0 K
18. Substance X has a heat of vaporization of 55.4 kJ/mol at its normal boiling point (423 °C).  For the process X (l) ® X (g) at 1 atm and 423 °C calculate the value of:
 DSuniv.
[A] 79.6 J/K×mol
[B] 0
[C] 103 J/K×mol
[D] -103 J/K×mol
[E] -79.6 J/K×mol
19. The enthalpy of vaporization of ethanol is 38.7 kJ/mol at its boiling point (78°C).
 Calculate the value of DS when 1.00 mole of ethanol is vaporized at 78.0°C and 1.00 atm.
[A] 0
[B] 496 J/K mol
[C] -496 J/K mol
[D] 110. J/K mol
[E] -110. J/K mol
20. For a spontaneous exothermic process, which of the following must be true?
[A] DS must be positive.
[B] DS must be negative.
[C] DG must be positive.
[D] Two of these must be true.
[E] None of these (a-c) must be true.
21. Consider the following processes:

For how many of these is DS positive?
[A] 2
[B] 1
[C] 0
[D] 4
[E] 3
22. Determine DG° for the following reaction:
	CH4(g) + 2O2(g) ® CO2(g) + 2H2O(l)

[A] 207.7 kJ
[B] 106.3 kJ
[C] 130.4 kJ
[D] 817.9 kJ
[E] 943.1 kJ
23. At 1 atm, liquid water is heated above 100°C.
 DSsurr for this process is

[A] equal to zero.
[B] less than zero.
[C] greater than zero.
[D] more information is needed to answer this question.
[E] none of these (a-d)

Reference: 6.4
[1] [B]

Reference: 6.3
[2] [A]

Reference: 6.1
[3] [E]

Reference: 6.1
[4] [B]

Reference: 6.2
[5] [E]

Reference: 6.2
[6] [C]

Reference: 6.2
[7] [C]

Reference: 6.1
[8] [E]

Reference: 6.3,4
[9] [B]

Reference: 6.3
[10] [C]

Reference: 6.2
[11] [B]

Reference: 6.2,4
[12] [A]

Reference: 6.2
[13] a) exothermic;  b) 52.2 kJ;  c) 0.0388 g Al

Reference: 6.4
[14] [E]

Reference: 6.2
[15] [B]

Reference: 16.1,5
[16] decrease in entropy

Reference: 16.4-6
[17] [D]

Reference: 16.4
[18] [B]

Reference: 16.4
[19] [D]

Reference: 16.4
[20] [E]

Reference: 16.5
[21] [E]

Reference: 16.6
[22] [D]

Reference: 16.3,4
[23] [B]