A catalyst is a substance that increases the rate of a chemical reaction, without being used up in the process. This means that the mass of a catalyst remains the same before and after the reaction. Also, only a small amount is required to increase the rate of reaction.
Catalysts are very useful in chemistry because they allow us to carry out reactions more quickly, without needing to increase the temperature or pressure. As a result, using catalysts helps to reduce costs. Also, as catalysts are not used up in the reaction, we can use them over and over again.
When writing chemical equations, catalysts are not included in the reaction, since they are not consumed. Instead, you may see catalysts written over the reaction arrow in equations.
Reaction profiles (energy level diagrams) are a useful tool for understanding the energy changes that occur during chemical reactions. In a reaction profile:
The energy of the reactants is shown on the left-hand side of the profile, while the energy of the products is shown on the right-hand side.
The activation energy is the minimum energy required for a reaction to occur. If the energy of the colliding particles is less than the activation energy, the reaction will not occur. Therefore, the activation energy acts as a barrier that must be overcome for the reaction to proceed.
Catalysts increase the rate of reaction by providing an alternative pathway for the reaction that has a lower activation energy. This means that the reacting particles do not require as much energy to have a successful collision. As a result, there are more successful collisions per unit of time.
Reaction profiles can also show the effect of a catalyst on the activation energy. The presence of a catalyst can be represented by a lower activation energy barrier in the reaction profile. This indicates that the catalyst provides an alternative pathway for the reaction that requires less energy to proceed.