Collision theory

The rate of a reaction is determined by finding the rate of change of reactant/product with respect to time.

For a successful reaction to occur,

  • The reactant particles must collide
  • The particles must collide with sufficient energy for the reaction to occur, so that there is sufficient energy to break the bonds in the particles
  • The particles must collide in a specific orientation, to facilitate the proper breaking and forming of bonds.

When reactant particles collide, the kinetic energy of the particles is transformed into potential energy, since the bonds begin to break. This increases the total potential energy of the system.

If there is sufficient energy, bonds will break and begin to form, which in turn decreases the potential energy of the system.

It follows that there must be a maximum level of potential energy. This stage is called the transition state, which is:

  • When the highest potential energy state is reached
  • When bonds are both being broken and formed
  • Is temporary and unstable

The minimum amount of energy required for the reaction to occur is called activation energy. The lower the Ea, it the reaction will probably take place faster at room temperature, and the higher it is, the slower.

Exothermic reaction

  • The products have less potential energy than the reactants
  • Heat is thus released to the environment
  • ΔH (change in enthalpy) is negative value
  • Ea is lower for the forward reaction

exothermic reaction

Endothermic reaction

  • The products have more potential energy than the reactants
  • Heat is thus taken from the environment
  • ΔH is positive
  • Ea is greater for the forward reaction

endothermic reaction


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