Collision Theory (Oxford AQA International A Level Chemistry)

Collision Theory

• The collision theory states that for a chemical reaction to take place the particles need to collide with each other in the correct orientation and with enough energy

Collision Theory table

• An ineffective collision is when particles collide in the wrong orientation or when they don’t have enough energy and bounce off each other without causing a chemical reaction

Increase in reaction rate

• The collision frequency is the number of collisions per unit time

• When more collisions per unit time take place, the number of particles with energy greater than the E_a increases

• This causes an increase in the rate of reaction

• Even though particles collide with each other in the same orientation, if they don’t possess a minimum energy that corresponds to the E_a 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 E_a of that reaction

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 (E_a)

Exothermic reactions

• In exothermic reactions the reactants are higher in energy than the products

Endothermic reactions

• In endothermic reactions the reactants are lower in energy than the products

• Therefore, the E_a in endothermic reactions is relatively large compared to an exothermic reaction