A catalyst does not change the position of equilibrium, so it does not change the equilibrium yield of product.A catalyst provides an alternative pathway with a lower activation energy. The same pathway is used in both directions, so the activation energy of the forward reaction and of the backward reaction are both lowered by the same amount.As a result, the catalyst increases the rates of the forward and backward reactions by the same factor. The balance between them does not change, so:• the equilibrium concentrations are the same as without a catalyst
• the value of Kc is unchanged
• equilibrium is reached more quickly.
This means a catalyst cannot be used to increase the percentage of reactants converted to products at equilibrium. It is still very valuable in industry, because a reaction that reaches equilibrium faster produces more product per hour.Catalysts also allow a process to run at a lower temperature while keeping an acceptable rate. For an exothermic reaction such as the Haber process, a lower temperature gives a higher equilibrium yield, so the catalyst helps the yield indirectly, by making it practical to operate at a lower temperature. The iron catalyst itself does not shift the equilibrium.Exam tip: in a question listing changes of conditions, the answer for a catalyst is always 'no effect on the position of equilibrium, but equilibrium is reached faster'.
• the value of Kc is unchanged
• equilibrium is reached more quickly.
This means a catalyst cannot be used to increase the percentage of reactants converted to products at equilibrium. It is still very valuable in industry, because a reaction that reaches equilibrium faster produces more product per hour.Catalysts also allow a process to run at a lower temperature while keeping an acceptable rate. For an exothermic reaction such as the Haber process, a lower temperature gives a higher equilibrium yield, so the catalyst helps the yield indirectly, by making it practical to operate at a lower temperature. The iron catalyst itself does not shift the equilibrium.Exam tip: in a question listing changes of conditions, the answer for a catalyst is always 'no effect on the position of equilibrium, but equilibrium is reached faster'.