Activation Energy
- For a reaction to take place, the reactant particles need to overcome a minimum amount of energy
- This energy is called the activation energy (Ea)
- In exothermic reactions, the reactants are higher in energy than the products
- In endothermic reactions, the reactants are lower in energy than the products
- Therefore, the Ea in endothermic reactions in endothermic reactions is relatively larger than in exothermic reaction
Exothermic reaction pathway diagram
The reactants are higher in energy than the products in an exothermic reaction, so the energy needed for the reactants to go over the energy barrier is relatively small
Endothermic reaction pathway diagram
The reactants are lower in energy than the products in an endothermic reaction, so the energy needed for the reactants to go over the energy barrier is relatively large
- Even though particles collide with each other in the same orientation, if they don’t possess a minimum energy that corresponds to the Ea of that reaction, the reaction will not take place
- Therefore, for a collision to be effective the reactant particles must collide in the correct orientation AND possess a minimum energy equal to the Ea of that reaction
Examiner Tip
The activation energy is the energy needed to ‘activate’ the reactant particles in order for them to collide effectively and cause a chemical reaction.