Name________________________

Use the thermodynamics table in your book to look up any enthalpy, entropy or free energy values needed.

1. Predict the sign of the entropy change for the following reaction:

Nitrogen gas reacts Hydrogen gas to produce ammonia gas.

2. Given the following data, calculate the free energy of the reaction and state if it is spontaneous or non spontaneous.

D H= +16kJ/mol, D S = 50J/K, T= 600K

3. The heat of fusion for actinium is 10.50kJ/mol. The entropy of fusion is 10.6 J/mol K. Calculate the melting point of actinium. (Hint) the melt point is an equilibrium between the solid and liquid phase, Therefore D G = ??????

4. Calculate D H for the following reaction at 25°C: D H_f for FeCl₃ = -400kJ/mol

6Cl_2(g) + 2Fe₂O₃ ---> 4FeCl₃ + 3O_2(g)

5. Calculate D S for the reaction in question #4

6. Using the answers from problem #4 and #5, calculate the free energy of the reaction.

7. Calculate the equilibrium constant for the reaction in question #4

8. Given the following reactions

N₂ + 2O₂ ---> 2NO₂ D G = -85kJ

2NO + O₂ ---> 2NO₂ D G = -60kJ

Calculate D G for N₂ + O₂---> 2NO

9. Given Kb for ammonia at 298K is 8.5x10^-6 calculate D G° for the following reaction:

NH_3(g) + H₂O_(l) <--> NH₄⁺_(aq) + OH^-_(aq)

9b . What is the value of D G at equilibrium?

9c, What is the value of D G when [NH₃] = 0.20 M, [NH₄⁺] = 0.20M and [OH^-] =0.10M

The following reaction is one that contributes significantly to the formation of photochemical smog.

2NO + O₂ --> 2NO₂ D H = -114.1 kJ, D S° = -146.5J/K 

10a. Calculate the heat released when 85.1 g of NO₂ is produced

10b. For the reaction at 25°C, the value of the standard free energy change, D G°, is -70.4kJ. Calculate the value of the equilibrium constant, Kc, for the reaction at 25°C.

10c. Indicate whether the value of D G° would become more negative, less negative, or remain unchanged as the temperature is increased. Justify your answer.

10d. Give the standard molar entropy, S° for NO = 210.8J/mol K and NO₂ = 240.1 J/mol K calculate S° for O₂ at 25°C

11. If D H is exothermic and D S is decreasing What should be done to the temperature to make the reaction spontaneous?

(a) increase the temp. (b) decrease the temp. (c) no temp will make the reaction spont.

(c) the reaction is spont. at all temp.

12. If D H is endothermic and D S is increasing what should be done to the temperature to make the reaction spontaneous?

(a) increase the temp. (b) decrease the temp. (c) no temp will make the reaction spont.

(c) the reaction is spont. at all temp.

Answers:

1) negative,

2) Spont.

3)990.5 K or 717.6C

4) +44.4

5) +389J/molK

6) -70.3

7) 2.4x10²⁸

8) -25

9) +28.9

9b) zero

9c) 23.2

11)B

12) A