Homogeneous catalysis: Offering an easier path

The second type of catalyst is a homogeneous catalyst — one that is in the same phase as the reactants. It provides an alternative mechanism, or reaction pathway, that has a lower activation energy than the original reaction. For an example, check out the decomposition reaction of hydrogen peroxide:

2H₂O_2(l) → 2 H₂O_(l) + O_2(g)

This is a slow reaction, especially if you keep the hydrogen peroxide cool in a dark bottle. The hydrogen peroxide in that bottle in your medicine cabinet may take years to decompose. But if you put a little bit of a solution containing the ferric ion in the bottle, the reaction will be much faster, even though it’ll be a two-step mechanism instead of a one-step mechanism:

If you add the two preceding reactions together and cancel the species that are identical on both sides, you get the original, uncatalyzed reaction (species to be cancelled are bolded):

The ferric ion catalyst was changed in the first step and then changed back in the second step. This two-step catalyzed pathway has a lower activation energy and is faster.