Glossary activated complex. An intermediate structure formed in the conversion of reactants to products. R is the universal gas constant . A substance that increases the rate of a chemical reaction, without being consumed or produced by the reaction. Catalysts speed both the forward and reverse reactions, without changing the position of equilibrium .
Enzymes are catalysts for many biochemical reactions.
The average number of collisions that a molecule undergoes each second. A theory that explains reaction rates in terms of collisions between reactant molecules. Compare with net chemical reaction . A reaction that occurs in a single step. Equations for elementary reactions show the actual molecules, atoms, and ions that react on a molecular level.