Reaction rate is the speed at which the reaction proceeds toward equilibrium. For an enzyme catalyzed reaction, the rate is usually expressed in the amount of product produced per minute.
Reaction rate is governed by the energy barrier between reactions and products. In general, energy must be added to the reactants to overcome the energy barrier. This added energy is termed "activation energy," and is recovered as the reactants pass over the barrier and descend to the energy level of the products.
Enzymes can accelerate the rate of a reaction. Enzymes are biological catalysts. Catalysts accelerate the rates of reactions by lowering the activation energy barrier between reactants and products. For a diagram comparing the energy barrier of a noncatalyzed reaction to a catalyzed reaction, see the tutorial for problem 1.
Temperature can have an important effect on enzyme activity and reaction rates. At low temperature, warming usually increases the rate of an enzyme catalyzed reaction because the reactants have more energy, and can more readily achieve the activation energy level. However if the temperature is raised too high, it is possible to denature the enzyme, causing a disruption of tertiary structure and loss of catalytic activity.