ABSTRACT To catalyze a reaction, an enzyme will grab on (bind) to one or more reactant molecules. In this experiment we examined how increasing the volume of the extract added to the reaction would affect the rate of the reaction. The enzyme used was horseradish peroxidase which helps catalyze hydrogen peroxide. Using different pH levels, the absorbance rate of the reaction was measured to see at which condition the enzyme worked best. The rates of absorption were calculated using a spectrophotometer in 20 second intervals up to 120 seconds. It was hypothesized that the optimal pH for the enzyme was pH 7 while the 1.0 ml peroxidase would have the best reaction rate. At the end of the experiment the results prove the hypothesis to be incorrect. INTRODUCTION Enzymes are proteins that allow a reaction to speed up. These proteins are made up of monomers known as amino acids. Each amino acid is made up of an amino group, a carboxyl group and a side chain (Reece, J. B., Urry, L. (2016). Campbell biology. Boston Pearson). Enzymes work by lowering the activation energy of the reaction making the reaction produce faster. Enzymes begin to catalyze chemical reactions with the binding of the substrate to the active site on the enzyme. The products are released from the enzyme surface to regenerate the enzyme for another reaction cycle. The active site has a unique geometric shape that is complementary to the shape of a substrate molecule, similar to the fit of puzzle pieces.