Catalysts Do Not Shift the Position of Equilibrium

What students typically write

“The catalyst shifts the equilibrium to the right to make more product.” Or: “Adding a catalyst increases the yield because it speeds up the forward reaction.”

Students learn that catalysts speed up reactions and that Le Chatelier’s principle describes shifts in equilibrium. They combine these two ideas incorrectly and conclude that catalysts must shift the equilibrium.

Why it is wrong

A catalyst provides an alternative pathway with lower activation energy. Crucially, it does this for both the forward and the reverse reactions. Both speeds increase by the same factor. Since dynamic equilibrium is defined by equal forward and reverse rates, accelerating both equally does not change the point at which they balance.

The result: equilibrium is reached faster, but the proportions of reactants and products at equilibrium are identical with or without the catalyst.

Le Chatelier’s principle applies to changes in concentration, temperature, and pressure. It does not apply to catalysts. Adding a catalyst is not a stress on the equilibrium, so there is no shift to counteract.

What the mark scheme actually wants

A typical question: “State and explain the effect of a catalyst on the position of equilibrium.” [2]

Marking points:

1. No effect on the position of equilibrium / the equilibrium position is unchanged (1 mark)
2. The catalyst increases the rate of both the forward and reverse reactions equally (1 mark)

An answer that says the catalyst shifts the equilibrium loses both marks.

Worked example: wrong vs right

Question: In the Haber process, explain the role of the iron catalyst. [2]

Wrong answer: “The iron catalyst shifts the equilibrium to the right so more ammonia is produced, increasing the yield.” This scores 0/2. It makes the specific error the question is testing for.

Right answer: “The iron catalyst increases the rate at which equilibrium is reached (1) by providing an alternative pathway with lower activation energy for both the forward and reverse reactions. It does not change the position of equilibrium or the yield (1).” This scores 2/2.

How to avoid this mistake

Keep two lists separate in your mind:

Things that shift the position of equilibrium: changes in concentration, changes in temperature, changes in pressure (for gaseous reactions).

Things that do NOT shift the position of equilibrium: catalysts, adding an inert gas at constant volume.

When a question asks about a catalyst and equilibrium, the answer is always: equilibrium is reached faster, but the position is unchanged.

For the full treatment of Le Chatelier’s principle and equilibrium shifts, see reversible reactions and equilibrium. The rate of reaction page covers how catalysts affect reaction rates.