Question

3. (20 pts) a. Consider the following reaction: PC15(g) z PC13(g) + Cl2(g) Using the following data find the AH°, 45°, and AG° at 534 K. Kºp 0.245 1.99 4.96 9.35 T(K) 485 534 556 574 b. For the reaction above state whether the equilibrium shifts to the left or the right (or neither) when the following changes are made in an equilibrium mixture at 25 °C. 1. Tis decreased at constant P 2. Vis decreased at constant T Some PCls is removed at constant T and V 4. Helium gas is added to the mixture at constant T and V 5. Helium gas is added to the mixture at constant T and P 3.

Answer 1

3.(a) Using given data the answers of the problem are :

Ko 0.245 1.99 4.96 9.35 T(K) 485 534 556 674 Psy - Paz (g) + Cl2(g) We know that A6 = 44 - TAS and AG = - RT like Hence, OG = -8.314x 534X hn 1.99 I = 3055 s = 3:05 kJ at 534K Again, we know that In KP2 = Ah (T2-T ) 05, H = R ( Tito ) - Kape I TT2 T2-T WS 1 = 8.314x 534x485 in/1.99 1534-4B5) 10.245 = 92.05 kJ at 534K 44 - AG = 92.05-3.05 KJ IK 534 = 0.167 kJ/K Honce, As =

b.

1. If T is decreased at constant P , the equilibrium will shift towards left.

2. V is decreased at constant T, the equilibrium will shift towards left.

3. If some PCl_{​​​​5} is removed at constant T and volume, the equilibrium will shift towards left.

4. Helium gas is added to the mixture at constant T and V, according to La Chatelier's principles -

The equilibrium will remain unchanged.

5. He is added to the mixture at constant T and P, according to La Chatelier's principles -

The equilibrium will shift towards right direction as ∆n is positive for the reaction.