Collision Theory

7.4

Collision Theory

Collision theory is used to explain how the factors (size, concentration, temperature, catalyst and pressure) affect the rate of reaction.
Particles are constantly moving at random and collide with each other.
The collision theory states that a chemical reaction may occur from the collision of the particles.
However, not all collision causes a chemical reaction.
Only effective collisions cause a chemical reaction.
The condition for effective collision is as follows;
- Particles must collide in the correct orientation.
- Particles must possess the energy equal or more than the activation energy.
Activation energy: the minimum energy needed by reactant for a chemical reaction to occur.
Energy profile diagram: a diagram showing the change of energy in a chemical reaction.

Factors affecting	Explanation
Size of the reactant	Size of reactant smaller Higher total exposed surface area Higher collision frequency Higher effective collision frequency Higher rate of reaction
The concentration of the reactant	A higher concentration of liquid reactant A higher number of particles per unit volume Higher collision frequency Higher effective collision frequency Higher rate of reaction
Temperature of reaction	A higher temperature of the reaction The higher kinetic energy of particles Higher collision frequency Higher effective collision frequency Higher rate of reaction
Catalyst	Presence of catalyst Lowers activation energy of the chemical reaction Higher collision frequency Higher effective collision frequency Higher rate of reaction
Pressure	The higher pressure of the reaction Higher collision frequency Higher effective collision frequency Higher rate of reaction