Question

An enzyme affects the rate of a chemical reaction by A. decreasing the free energy change of the reaction. B. increasing the free energy change of the reaction. C. lowering the energy of activation of the reaction. D. displacing the equilibrium constant. E. raising the energy of activation of the reaction.

Answer 1

Answer C. An enzyme affects the rate of a chemical reaction by lowering the energy of activation of the reaction.

Enzymes are biological catalysts. They work by lowering the activation energy of biochemical reaction thus enabling the reaction to occur at a greater rate than it could under the temperature, pressure and environment of a biological environment.

Activation energy is the minimum energy which must be available to a chemical system with potential reactants to result in a chemical reaction.

For example in a general chemical reaction A+BàC. If the energy of the system A+B is greater than the energy of system C then the overall reaction will give out energy. This will be the form of heat or will be captured in a high energy compound such as ATP. If the energy of A+B is less then C then the reaction will require an input of energy. However this describes the overall energy states of the substrates and products.

In either of the cases described above A and B must be raised to a high energy state for the reaction to occur.
This energy required for a reaction to occur is called as activation energy. As we can’t heat a biochemical reaction of course so enzymes lower this activation energy. The way they do this is quite complex and there are different types of mechanisms. In many case the substrate(s) and enzymes for enzyme - substrate complexes through binding at the active site of the enzyme. Then enzyme - product complexes are formed before the product is released. The enzyme is not consumed during these reactions and that is one of the properties of a catalyst. These complexes bring substrates into very close proximity.