Why do catalysts speed up reactions without changing the equilibrium?

Answer 1

How catalysts work

1. A catalyst provides an alternative reaction pathway that has a lower activation energy (Ea).
2. Because the barrier is lower, more reactant molecules have enough energy to react per unit time, so the reaction rate increases.

Why equilibrium isn’t changed

1. Catalysts speed up both the forward and reverse reactions equally.
2. The equilibrium position depends on ΔG (Gibbs free energy), not on activation energy.
3. Since a catalyst doesn’t change ΔG, it doesn’t favor products or reactants, just helps the system reach equilibrium faster.

Answer 2

One way to think about the effect of a catalyst is like a highway.

If we're trying to get from one city to another, you could go multiple routes.

A) If you take the backroads and avoid the highways, you'll still reach your destination, but you might have to take a lot of twists and turns that encounter many traffic lights that slow you down.

B) If you take the highway, you might be able to go directly two your destination encountering much less traffic that would slow you down, thus you get to your destination quicker.

Like highways, catalysts offer alternative chemical pathways (as opposed to highways offering alternative driving roadways) to reach the end of the reaction.

In terms of the equilibrium aspect. People may like City 1 as opposed to City 2 as it might have a more enjoyable lifestyle, thus more people will spend time in City 1 as opposed to City 2. Whether or not the highway exists, people will still spend more time in City 1, the existence of the highway just makes the process easier and faster to get to City 1.

Hope that helps!

Answer 3

Catalysts lower the activation energy of both the forward and reverse reactions, helping the system reach equilibrium faster — but they don’t shift its position. That’s because catalysts don’t affect the energy difference between reactants and products — only how quickly the system gets there. Understanding this subtle concept is key in both AP Chemistry and college-level courses.