Collision Theory | Chemistry for Grade 11 (IGCSE) PDF Download

What is Collision Theory?

• According to collision theory, for a reaction to occur:
  • Particles must collide with one another.
  • Collisions must possess adequate energy to initiate a reaction, enough to break existing bonds.
  • The minimum energy required for colliding particles to react is termed the activation energy.
• Collisions that lead to a reaction are termed successful collisions:
  • If the colliding particles possess sufficient energy (exceeding the activation energy), they react, resulting in a successful collision.
• Not all collisions lead to chemical reactions:
  • Many collisions simply cause the particles to rebound off each other.
  • Collisions that do not result in a reaction are termed unsuccessful collisions.
• Unsuccessful collisions occur when the colliding species lack the necessary energy to break bonds:
  • They collide with energy below the activation energy threshold.

Diagram showing a successful and an unsuccessful collision 

• Enhancing the number of successful collisions increases the proportion of reactant particles combining to form product molecules.
• The frequency of successful collisions hinges on:
  • The density of particles within a given volume, as higher particle counts result in more frequent successful collisions.
  • Collision occurrence rate, where a greater number of collisions per second leads to a higher frequency of successful collisions.
  • Particle kinetic energy, where higher kinetic energy levels lead to more collisions surpassing the activation energy threshold, as faster-moving particles result in more frequent successful collisions.
  • Activation energy levels, where higher activation energies lead to fewer collisions surpassing the threshold, resulting in fewer successful collisions.
• These factors collectively influence the reaction rate, determined by the rate of successful collisions per unit time.