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CHM 112
Chapter 17 Worksheet: Thermodynamics
Name: ______________________
Q1. Which of the following processes are spontaneous and which are non spontaneous?
a) spreading of the fragrance of perfume/ air freshener in a room
b) cleaning your room
c) 2H2O (l) → 2H2 (g) + O2 (g) (at room temperature, 1 atm pressure)
d) Building a house of cards
Q2.
Predict the sign of entropy change (positive or negative) for the following systems:
a) a lake freezing
b) SO2(g) + CaO(s) → CaSO3(s)
c) NH3(g) + HCl(g) → NH4Cl (s)
d) 4 CO2 (g) + 2 H2O (g) → 2 C2H2 (g) + 5 O2(g)
e) N2H4 (g) → N2(g) + 2 H2(g)
Q3.
Using the values for standard molar entropies (S°) from the Appendix in your text book, calculate ΔS° for the following
reactions.
a) CH3OH (l) → CO (g) + 2 H2(g)
b) C2H5OH(l) + O2(g) → HC2H3O2 (l) + H2O (l)
c) 2CH4(g) → C2H6 (g) + H2(g)
Q4.
For the reaction: 2Al(s) + 3/2 O2(g)  Al2O3(s), ∆Horxn = – 1617 kJ/mol and ∆Gorxn = –1577 kJ/mol. Use this data to
calculate ∆S° reaction at 298 K.
Q5.
What is the minimum temperature required for the spontaneous conversion of CCl4(l) to CCl4(g) when ∆H°(vap) is 57.3
kJ/mol and ∆S°(vap) is 164 J/(mol K) ?
Q6. Using the data in the appendix of your text book, calculate the standard Gibbs free energy change (ΔG°) at 25°C for the
following reactions. In each case, indicate whether the reaction is spontaneous or not at that temperature.
a) 2HCl (g) ⇆ H2 (g) + Cl2(g)
b) 2 AgCl(s) + Ca(s) ⇆ CaCl2 (s) + 2 Ag (s)
c) SO3(g) + H2O (l) ⇆ H2SO4 (l)
Q7. For each of the reactions listed in Q6, calculate the value of the equilibrium constant K (assuming 1 mole at 25°C).
a)
b)
c)
Q8.
Given the following data,
4 NO(g)  2 N2O(g) + O2(g)
∆G° = – 139.56 kJ
2 NO (g) + O2(g)  2 NO2 (g)
∆G° = – 69.70 kJ
Calculate ∆G° for the following reaction:
2 N2O(g) + 3 O2(g)  4 NO2 (g)
Q9. Write the reaction for the vaporization of water. Calculate the ΔG⁰rxn at 25.0⁰C.
Is the reaction spontaneous at 25.0⁰C?
Use the values of ΔH⁰f and S⁰ to estimate the value of ΔG⁰rxn at 125⁰C. Is the reaction spontaneous at this temperature? Why?
Q10.
Consider the reaction:
2 NO2 (g) ⇄ N2O4 (g)
a) Using the data in your textbook, calculate the Gibbs free energy change (ΔG°) for the reaction at 298 K.
b) Calculate the value of Keq at 298 K.
c) Calculate ΔG at 298 K when the partial pressures for NO2 and N2O4 are 10.5 and 0.50 atm respectively.
Q11.
Consider the reaction:
C(s) + 2 H2 (g) → CH4 (g)
a) Using the data in your textbook, calculate the standard Gibbs free energy change (ΔG°) for the reaction at 298 K.
b) Estimate ΔG˚ for the reaction at 400 K. (Is the reaction more or less spontaneous at high temperature?)
c) Calculate the value of ΔG at 298 K when the partial pressures of CH4 and H2 are 25.5 atm and 1.00 atm
respectively. Predict what should happen using Le Chatelier’s principle. Is the calculated result consistent with the
predicted result?
d) Above what temperature will this reaction be nonspontaneous?
Q12. At what temperature will the reaction become nonspontaneous?
FeO(s) + CO(g) → CO2(g) + Fe(s)
ΔH = -11.0 kJ; ΔS = -17.4 J/K
The following are multiple choice questions:
13. Melting of a solid is an example of a process for which
(A) ∆H, ∆S, and ∆G are positive at all temperatures.
(B) ∆H and ∆S are positive.
(C) ∆G is negative at low temperatures, positive at high temperatures.
(D) ∆H = ∆S
14. For the following process: 2I(g)  I2(s)
(A) ∆H is + and ∆S is + for the reaction.
(B) ∆H is – and ∆S is – for the reaction.
(C) ∆H is + and ∆S is – for the reaction.
(D) ∆H is – and ∆S is + for the reaction.
(E) ∆G is + for all temperatures
15. A reaction is spontaneous at all temperatures if
(A) ∆H and ∆S are both positive.
(B) ∆H and ∆S are both negative.
(C) ∆H is positive and ∆S is negative.
(D) ∆H is negative and ∆S is positive.