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Does adding a catalyst shift equilibrium

Adding a catalyst does not shift the position of equilibrium; it only speeds up the rate at which equilibrium is reached. The equilibrium constant K remains the same because the catalyst lowers the activation energy for both the forward and reverse reactions equally.

Chemistry · Chemical equilibrium

A catalyst provides an alternative pathway with lower activation energy for both directions of a reversible reaction. For example, in the Haber process N₂+3H₂⇌2NH₃, iron speeds up the formation of NH₃ and its decomposition, but the ratio of product to reactant concentrations at equilibrium stays unchanged.

Why the equilibrium constant stays the same

Key reasons the equilibrium position is unaffected:

  • Catalyst lowers activation energy for forward and reverse reactions equally
  • Both forward (kfk_f) and reverse (krk_r) rate constants are multiplied by the same factor
  • Equilibrium constant K = kfk_f/krk_r therefore does not change

How to see the effect experimentally:

  1. 1Measure concentrations of N₂, H₂, and NH₃ over time without a catalyst until they stop changing
  2. 2Add iron catalyst and repeat the measurement under identical temperature and pressure
  3. 3Notice that the same final concentrations are reached faster

Catalyst effect on rate constants (arbitrary units):

Conditionk_f (s⁻¹)k_r (s⁻¹)
No catalyst0.010.005
With catalyst0.100.05

Check yourself

Which statement correctly explains why a catalyst does not change the equilibrium constant?

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