Practice Problem 7

Predict the effect of the following changes on the reaction in which SO₃ decomposes to form SO₂ and O₂.

2 SO₃(g) 2 SO₂ (g) + O₂ (g) H^o = 197.78 kJ

(a) Increasing the temperature of the reaction.

(b) Increasing the pressure on the reaction.

(c) Adding more O₂ when the reaction is at equilibrium.

(d) Removing O₂ from the system when the reaction is at equilibrium.

Answer

(a) Because this is an endothermic reaction, which absorbs heat from its surroundings, an increase in the temperature of the reaction leads to an increase in the equilibrium constant and therefore a shift in the position of the equilibrium toward the products.

(b) There is a net increase in the number of molecules in the system as the reactants are converted into products, which leads to an increase in the pressure of the system. The system can minimize the effect of an increase in pressure by shifting the position of the equilibrium toward the reactants, thereby converting some of the SO₂ and O₂ into SO₃.

(c) Adding more O₂ to the system will shift the position of the equilibrium toward the reactants.

(d) Removing O₂ from the system has the opposite effect; it shifts the equilibrium toward the products of the reaction.