Presence of a Catalyst

Catalysts are substances that increase the rate of a reaction without changing the nature of the reactants or products. In other words, the overall reaction is the same with and without the catalyst, but with it, the reaction is faster. We will discuss more exactly how catalysts work in the Catalysis section.

Example: decomposition of hydrogen peroxide

Dilute aqueous solutions of hydrogen peroxide (H2O2) are one common topical antiseptic. Hydrogen peroxide decomposes to yield water and oxygen gas according to the equation: $$2H_2O_2\;(aq)\;\rightarrow\;2H_2O\;(l)+O_2\;(g)$$

Under typical conditions, this decomposition occurs very slowly. However, when dilute H2O2(aq) is poured onto an open wound, the reaction occurs rapidly, creating foam with the vigorous production of oxygen gas.

This difference is caused by substances (especially the well-named enzyme catalase) within the exposed tissues that catalyze the decomposition.