Enzymes speed up a chemical reaction by lowering the activation energy required for the reactants to come together and react. Activation energy refers to the energy that is needed to trigger a chemical reaction between two or more reactants. Some reactions require a great amount of activation energy, which acts as an energy barrier making it difficult for the reactants to come together and react. Enzymes reduce the energy needed for the reactants to come together, increasing the rate of the chemical reaction. Enzymes may work inthree different ways to speed up chemical reactions: 

• They may bring the reactants together making it easier for them to interact with each other instead of expending energy moving about until they collide at random. 
• They may guide the reaction towards a different pathway that requires lower activation energy. 
• They may position reactants correctly by binding them at the active site. This allows the reactants to interact with less energy as they won’t need to overcome intermolecular forces that would otherwise push them apart. 

The rate at which an enzyme speeds up a chemical reaction may be affected by temperature, ionic conditions, and the pH of the surroundings.