WJEC GCSE Chemistry Practice Exam

A catalyst works by providing an alternative reaction pathway that has a lower activation energy. This means the energy barrier that reactant molecules must overcome to reach the transition state is reduced, so more molecules have enough energy to react at any given temperature, speeding up the rate of the reaction. Importantly, the overall energy change of the reaction—the difference between the energies of reactants and products—stays the same, and the final products are unchanged. The catalyst itself is not consumed and simply facilitates the process. So the energy profile shows a lower peak (lower activation energy) while the overall enthalpy change remains the same.