Factors Affecting Rates of Chemical Reaction

 The collision theory shows that the rate of a chemical reaction depends on the frequency of the effective collisions between reactant particles. So any factor that can influence one or all following

·         The energy content of the particles

·         The frequency of the collision of the particles

·         The activation energy of the chemical reaction

Can also affect the rate of chemical rate and such factors are

·         Nature of reactants

·         Concentration / pressure(for gas) of the reactants

·         Surface area of reactants

·         Temperature of reaction mixture

·         Presence of light

·         Presence of catalyst

Nature of Reactants: The rate of reaction is affected by the chemical nature of the reactants because the energy content of different substances is not the same. For example, zinc reacts very fast with dilute hydrochloric acid to liberate hydrogen while gold does not show any sign of reaction.

Concentration of reactants: The frequency of collision increases with an increase in concentration, for gas, an increase in pressure increases the frequency of collision, while the decrease in concentration or pressure (for gas) decreases the frequency of collision of the reactant particles.

The surface area of the reactants: powdered marble chips react faster with dilute hydrochloric acid than granules. This is because the powdered marble chips have increased surface area in contact with the acid.

Temperature: Reactions are faster at high temperatures and slower at low temperatures. The increase in temperature of a system can lead to an increase in the rate of chemical reaction in two ways;

·         By increasing the energies of particles more than or equal to the activation energy

·         By increasing the average speed of all the reactant particles due to increased kinetic energy

These ways increase the number of effective collisions and help the reaction to be faster.

Light: Photochemical reaction like the reaction between hydrogen and chlorine is explosive in the presence of bright sunlight but negligible in the absence of light.

Catalyst: This is a substance that can change the rate of a chemical reaction without undergoing any change at the end of the reaction. Some catalysts can promote the rate of response while some retard the reaction. 

Rate of Chemical Reaction