What phrase best describes the effect of a catalyst on a chemical reaction? a. increases the volume of reactants b. decreases the reaction rate c. increases the temperature d. decreases the activation energy

A catalyst increases the rate of reaction by decreasing the activation energy. The correct answer is D. Catalysts are those substances that are used in reactions to speed up the process. An example of a catalyst might be iron, during the manufacture of ammonia within the Haber process.