Consider the reaction: 2NO(g) + O2(g) ⇌ 2NO2(g) ΔH = -114 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 speeds up both forward and reverse reactions equally, so it increases the rate without shifting the equilibrium position.

Why this answer is correct

Adding a catalyst provides an alternative reaction pathway with lower activation energy, increasing the rate of both forward and reverse reactions. It does not change the equilibrium constant or the position of equilibrium. Increasing temperature would shift the exothermic reaction toward reactants and also increase rate but would shift equilibrium. Adding helium at constant volume does not change partial pressures of reactants/products, so no effect on rate. Decreasing NO2 would shift equilibrium to the right but does not directly increase the rate of the forward reaction.

Example

In the Haber process, iron is used as a catalyst to increase the rate of ammonia synthesis without changing the equilibrium yield.