For the reaction CO(g) + 2H2(g) ⇌ CH3OH(g) (ΔH = -90 kJ/mol), which change will increase the rate of the forward reaction without necessarily shifting the equilibrium position?

Correct answer

A. Adding a catalyst

Principle or equation

A catalyst lowers the activation energy and increases both forward and reverse reaction rates equally, so the equilibrium position is not shifted. Other changes affect the rate and may also shift equilibrium.

Why this answer is correct

Adding a catalyst speeds up the attainment of equilibrium without changing the equilibrium composition. Increasing CH3OH concentration increases the reverse rate and shifts equilibrium left. Decreasing pressure lowers the rate and shifts equilibrium toward more gas moles (left). Increasing temperature increases both rates but shifts equilibrium in the endothermic direction (left for this exothermic reaction).

Example

In a closed vessel at equilibrium, adding a small amount of catalyst will cause the reaction to reach equilibrium faster but the final concentrations of CO, H2, and CH3OH remain the same as without the catalyst.