The effect of a catalyst on rate of reaction
- Catalysts are substances which speed up the rate of a reaction without themselves being altered or consumed in the reaction
- Normally only small amounts of catalysts are needed to have an effect on a reaction
- The mass of a catalyst at the beginning and end of a reaction is the same
- Catalysts do not form part of the chemical equation but they are sometimes seen above or below the reaction arrow:
N2 (g) + 3H2 (g) 2NH3 (g)
SO2 (g) + O2 (g) SO3 (g)
- Different processes require different types of catalysts but they all work on the same principle:
- They provide an alternative pathway for the reaction to occur
- The alternative pathway has a lower activation energy
Catalysts work by attracting reactant molecules on to the surface and so providing an alternate reaction pathway of lower energy
- Catalysis is a very important branch of chemistry in commercial terms as catalysts increase the rate of reaction (hence the production rate) and they reduce energy costs
- The transition metals are used widely as catalysts as they have variable oxidation states allowing them to readily donate and accept different numbers of electrons
- This is key to their catalytic activity
- Enzymes act as catalysts in biological systems
Examiner Tip
The effect of a catalyst on activation energy can be shown on a reaction profile.