Adding a catalyst
2 marks · HardExplain why the addition of a catalyst does not affect the position of equilibrium in a reversible reaction.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
Because a catalyst increases the rate of both the forward and reverse reactions by the same amount, so the relative amounts of reactants and products at equilibrium remain unchanged.
Also accept: A catalyst speeds up both reactions equally, so the proportion of products and reactants at equilibrium is not changed.
Common mistakes: Saying a catalyst pushes equilibrium to the right/left.; Omitting reference to both directions.
Show mark scheme and worked solution
Marking points
B1 · 1 mark · States catalyst increases both forward and reverse reaction rates equally.
B2 · 1 mark · States that the position of equilibrium/remains unchanged (relative amounts/products and reactants stay the same).
Worked solution
A catalyst works by providing an alternative pathway for the reaction, increasing the rate at which both forward and reverse reactions occur by the same proportion. Therefore, the equilibrium position does not shift since neither the forward nor the reverse reaction is favoured more than the other.