AP/IB Chemistry – Chapter 16 TestName:

Thermodynamics & Spontaneity

Multiple Choice: Circle the letter of the best response:

  1. For which process is ∆S negative?

a)Evaporation of 1 mol of CCl4(l)

b)Mixing 5 mL ethanol with 25 mL water

c)Compressing 1 mol Ne at constant temperature from 1.5 atm to 0.5 atm

d)Raising the temperature of 100 g Cu from 275 K to 295 K

e)Grinding a large crystal of KCl to powder

  1. A chemical reaction is most likely to be spontaneous if it is accompanied by

a)Increasing energy and increasing entropy

b)Lowering energy and increasing entropy

c)Increasing energy and decreasing entropy

d)Lowering energy and decreasing entropy

e)None of these (a-d)

  1. Assume that the enthalpy of fusion of ice is 6020 J/mol and does not vary appreciably over the temperature range 270-290 K. If one mole of ice at 0 oC is melted by heat supplied from surroundings at 285. K, what is the entropy change in the surroundings, in J/K

a)+22.1

b)+21.5

c)0.0

d)-21.5

e)-22.1

  1. For a spontaneous exothermic process, which of the following must be true

a)∆G must be positive

b)∆S must be positive

c)∆S must be negative

d)Two of the above must be true.

e)None of the above (a-c) must be true.

  1. For the process CHCl3(s)  CHCl3(l), ∆Ho = 9.20 kJ mol-1 and ∆So = 43.9 J mol-1 K-1. What is the melting point of chloroform?

a)–63 oC

b)210 oC

c)5 oC

d)63 oC

e)–5 oC

  1. Consider the dissociation of hydrogen:H2(g)  2H(g)One would expect this reaction:

a)will be spontaneous at any temperature

b)will be spontaneous at high temperatures

c)will be spontaneous at low temperature

d)will not be spontaneous at any temperature

e)will never happen

Free Response:

Answer the following questions on your own piece of paper. Show all work and box answers. Skip two lines between each problem. Staple your page to the back of this sheet.

  1. The reaction represented below is one that contributes significantly to the formation of photochemical smog.

2 NO(g) + O2(g)  2 NO2(g)ΔHo = -114.1 kJ, ΔSo = -146.5 J K-1

a)Calculate the quantity of heat released when 73.1 g of NO(g) is converted to NO2(g).

b)For the reaction at 25 oC,

i)Calculate the value of the standard free-energy change, ΔGo .

ii)Indicate whether the value of ΔGo would become more negative, less negative, or remain unchanged as the temperature is increased. Justify your answer.

c)Use the data in the table below to calculate the value of the standard molar entropy, So, for O2(g) at 25 oC.

Compound: / Standard Molar Entropy, So (J K-1 mol-1)
NO(g) / 210.8
NO2(g) / 240.1

8.Answer the following questions about the thermodynamics of the reactions represented below.

Reaction X:

½ I2(s) + ½ Cl2(g)  ICl(g)ΔHof = 18 kJ mol-1ΔSo298 = 78 J K-1 mol-1

Reaction Y:

½ I2(s) + ½ Br2(l)  IBr(g)ΔHof = 41 kJ mol-1ΔSo298 = 124 J K-1 mol-1

(a)Is reaction X, represented above, spontaneous conditions? Justify your answer with a calculation.

(b)Explain why the standard entropy change is greater for reaction Y than for reaction X.

(c)For the vaporization of solid iodine, I2(s)  I2(g), the value of ΔHo298 is 62 kJ mol-1. Using this information, calculate the value of ΔHo298 for the reaction represented below.

I2(g) + Cl2(g)  2 ICl(g)

9.Consider the following reaction::

CH4(g) + 2 O2(g)  CO2(g) + 2 H2O(l)

(a)Using the values of free energy of formation in Appendix 4, determine ΔGo for the reaction.

(b)Is the reaction spontaneous? Justify your response.