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Why does a catalyst speed up both the forward and reverse directions of a reversible reaction?

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dissociation of E–N — reaction mechanism Possible energy diagram for the dissociation of a covalent molecule, E–N, into its ions E⁺ and N⁻ (see text).

A catalyst accelerates both the forward and reverse directions of a reversible reaction because the reverse reaction proceeds by the exact reversal of the steps that constitute the reaction mechanism of the forward reaction.1

By providing an alternative pathway with a lower activation energy, the catalyst facilitates the transformation of reactants into products and products back into reactants with equal efficiency. Because the catalyst lowers the energy barrier for the reaction in both directions, it increases the rate at which chemical equilibrium is reached.12

Crucially, because the catalyst accelerates both directions equally, it does not alter the position of the equilibrium itself; it only changes the speed at which that equilibrium state is attained.12