For the reaction 2SO2(g) + O2(g) ⇌ 2SO3(g), which change will increase the rate of the forward reaction but not necessarily shift the equilibrium position?

Correct answer

A. Adding a catalyst

Principle or equation

A catalyst lowers the activation energy, increasing both forward and reverse reaction rates equally, so equilibrium is reached faster but the equilibrium composition is unchanged. Other changes may affect rate and equilibrium differently.

Why this answer is correct

Adding a catalyst speeds up the attainment of equilibrium without changing the equilibrium constant or the position of equilibrium. Increasing volume decreases concentrations, which generally decreases reaction rate. Decreasing temperature may slow the rate (for an exothermic forward reaction, it shifts equilibrium but also reduces rate). Adding an inert gas at constant volume does not change partial pressures or concentrations, so it has no effect on rate or equilibrium.

Example

In the Haber process, iron catalyst is used to increase the rate without changing the equilibrium yield.