Temperature

• The temperature of a system affects the rate at which a chemical reaction takes place. This is because temperature can make molecules move faster or slower. The higher the temperature, the faster molecules can move. The faster-moving molecules have more energy and are more likely to result in a chemical reaction than molecules at lower temperatures and lower energy levels. Temperature can be destructive. For example, enzymes that are catalysts in many chemical reactions in the body can become denatured, or fall apart, when exposed to high temperatures lowering the rate of chemical reactions.
  
  

Enzymes

• Enzymes are catalysts within chemical reactions. The catalyst is neither created, changed or destroyed during the chemical reaction. The enzyme function within chemical reactions is to lower the level of activation energy. By lowering the required activation energy, more chemical reactions can occur than if no enzyme was present. Enzymes play crucial roles with many chemical reactions that occur within the human body. For instance, the enzyme pepsin occurs in the stomach and aids in chemical reactions to help break down food.
  
  

pH

• The pH scale is a scale to measure how acidic or basic a solution is based on a scale 0 to 14. The lower the number, the more acidic. In chemical reactions pH levels do not have a direct effect on the level of activation energy. However, if enzymes are present, the pH level may have a direct effect on the enzyme. Each type of enzyme occurs in a typical pH. For example, pepsin, which occurs in the stomach works best with acidic pH, such as 2 on the pH scale since it is in hydrochloric acid. If an enzyme encounters a different pH level, the enzyme can change shape or be broken down affecting the rate of the reaction.
  
  

Other Factors

• Even once the activation energy has been reached, other factors can also affect the rate of reactions. The concentration of molecules, which is how many molecules are within a system, also affects the rate of the reaction. If there are many molecules in the system and the activation energy is reached, the reaction will occur quickly. If the concentration is low, the reaction will take longer period of time to occur.