Chemical Equilibrium Questions

The formation of ammonia from its elements is an important industrial processs

3 H2(g)+ N2(g)  ↔2 NH3(g)

1. Does the reaction shift to the right or to the left, or does it remain unchanged when extra H2 is added?

(a) Shift left

(b) Shift right

(c) Unchanged

Answer: (b)

Explanation: According to Le Chatelier's' Principle, a system at equilibrium will shift to the direction that removes an added stress. In this case, the stress is the added H2. The reaction will therefore shift to the direction that removes or consumes H2, which is the forward reaction. The equilibrium will shift to the right, which is the direction of the forward reaction.

2. Does the reaction shift to the right or to the left, or does it remain unchanged, when the volume of the system is increased?

(a) Shift left

(b) Shift right

(c) Unchanged

Answer: (a)

Explanation: According to Le Chatelier's' Principle, a system at equilibrium will shift to the direction that removes an added stress. In this case, the stress is the increase in volume. The reaction will shift to the direction that increases the number of gas molecules to occupy the increase in volume. The left side of the equilibrium reaction has a total of 4 gas molecules (3 molecules H2(g) + 1 molecule N2(g)), while the right side has 2 molecules of NH3(g). This means that the equilibrium will shift to the left to form more gas molecules to compensate for the increase in volume.

For the equilibrium 2SO2(g) +O2(g)  ↔ 2 SO3(g), K has the following values:4.0x1024 at 300 k, 2.5x1010 at 500K, and 3.0x104at 700K. Is this the reaction exothermic or endothermic?

(a) Exothermic

(b) endothermic

Answer: (a)

Explanation: The equilibrium constant, K, of the reaction decreases with increasing temperature. The equilibrium constant is equal to the ratio of the equilibrium concentration of products over that of the reactants raised to their respective coefficients. If the values of K decreases with an increase in temperature, the products are less and less favored as the temperature is raised. This is only possible if heat is represented as a product of the reaction. If more heat is applied, the equilibrium will shift to the left towards formation of reactants. If heat is a product of the reaction, then the reaction is exothermic.