There are several factors influencing the rate of a chemical reaction. It is essential to understand and to be able to predict the conditions affecting the reaction rate.
A catalyst is a substance which alters the rate of a chemical reaction staying chemically unchanged at the end of the process. Catalysts increase the rate of a chemical reaction by lowering the reaction activation energy and reaching the equilibrium faster.
Catalase is a complex protein found in blood, with Fe(III) ion in its active site. Catalase has one of the highest turnover rates of all enzymes; one molecule of catalase catalyzes decomposition of millions of molecules of hydrogen peroxide.
Hydrogen peroxide, clear colorless liquid, is a very strong oxidizing agent. Hydrogen peroxide is a byproduct of metabolism, it breaks down into water and oxygen regardless of reaction conditions, and the catalyst used is only facilitating the breakdown.
Catalase protects the cells from high concentration of hydrogen peroxide, known as oxidative stress. Immediate reaction between blood and hydrogen peroxide is presented in this video. Reaction mixture foams intensively and blood at the bottom of the beaker turns colorless.
In reaction with blood, hydrogen peroxide decomposes vigorously into water and oxygen:
Decomposition is significantly slower without the presence of catalyst. In this reaction catalase acts as a catalyst, which is not being consumed in reaction. Large amount of liberated oxygen causes intense foaming of reaction mixture, while the colorless remaining at the bottom of the glass can be explained with hemoglobin oxidation.