Collision Theory

  • Particles in a fluid are always moving and colliding with one another. These particles do not react unless the conditions are right for a successful collision
  • Collision theory states that a reaction will not occur between two particles unless both particles collide at each other with at least a certain minimum amount of kinetic energy
  • The collision must take place between the parts of the molecule which will react with one another
  • Most collisions do not react either of the result of insufficient amount of energy or the molecule is in the wrong orientation for the molecules to react

Activation Energy (Ea)

  • The minimum amount of kinetic energy required for a particle to react is the Activation Energy
  • This energy is required to break the bonds within the reactant particles, which thus starts the reaction
  • Reactions with low activation energies are easier to start compared to ones that have high activation energies.
  • Activation Energy also explains why not all exothermic reactions can occur instantly at room temperature

Factors which affect Rate of Reaction

  • Increasing the concentration: more particles in a given volume will lead to more collisions as there is a greater chance of hitting another particle successfully. However, as the reaction continues more reactants will be used up and therefore there will be fewer reactants for the reaction to continue. The result being the rate of reaction decreases towards the end
  • Increasing the temperature: Each particle has more kinetic energy which increases the speed the particles move in. The result is that there are more collisions with more energy
  • Increasing the surface area of a solid Reactant: a greater surface area of a solid results in there being more of the solid’s particles available for collision with molecules of a gas/liquid.
  • Increasing the pressure of a gas reaction: Similar to increasing the concentration, either decreasing the volume of the reaction vessel or add more particles in a given volume will result in more successful collisions
  • Catalyst: a substance that offers an alternative route for the reaction with a lower activation energy