Speed at which a chemical reaction proceeds, in terms of amount of product formed or amount of reactant consumed per unit of time.
The reaction rate depends on the nature of the reacting substances and the type of chemical change, as well as temperature and pressure, especially if gas es are involved. In general, the reactions of ion s occur very rapidly, but those in which covalent bond s are formed or broken are slower. Catalyst s usually accelerate reaction rates. The prediction, measurement, and interpretation of reaction rates are subjects of the branch of chemistry known as chemical kinetics. See also mass action, law of .