How do catalysts change the rate of reactions without being involved in the reaction?

Question

How do catalysts change the rate of reactions without being involved in the reaction?

Answer 1

It is wrong to assume that catalysts are not involved in the reaction. Catalysts interact with the other reactants and are consumed in the sub-reactions, but are eventually re-established so that the amount of catalyst before and after the entire reaction remains unchanged. Try to imagine:

A + B + C --> AB + C

where C is the catalyst. A sub-reaction such as:

A + C --> AC

occurs, after which

AC + B --> AB + C

occurs, and the catalyst is re-established. This happens very quickly. The direct reaction

A + B --> AB

may have a tediously slow reaction rate. The addition of catalyst C increases the reaction rate since each of the sub-reactions

A + C --> AC

AC + B --> AB + C

have very fast reaction rates.

Answer 2

Basically, catalyts provide a surface for the reactants to collide with with so that they can be separated from the other elements in the compound and therefore catalyts eliminate the high amount of enrgy required for bond breaking and allow the substances to react at a lower energy. It is actually incorrect to say that catalysts are not involved in the reaction, you should say that they are not "consumed" in the reaction. You'll probably see questions asking you for the correct statement alot in tests and exams.