Factors Affecting Rate of Chemical Reactions
The rate of a chemical reaction is defined as the change in the concentration of the reactant or product per unit time. The Factors affecting the rate of reaction are summarized as below:
Concentration of Reactants
The rate of reaction generally increases with increase in concentration of the reactants.
Temperature
Generally increase in temperature increases the rate of reaction. When the temperature increases, the reactant molecules acquire higher energy and can easily form the products. Cooked food gets spoilt quickly during summer than winter. Souring of milk is faster in summer. These are all due to the fact that the chemical reactions responsible for these changes take place faster at higher temperatures.
Presence of Light
There are certain reactions which take place or are accelerated by the absorption of light by the reactants. Such reactions are known as photochemical reactions. These reactions do not occur if the reactants are shielded from light. The combination of hydrogen and chlorine to produce hydrogen chloride does not take place at measurable rate in the dark. The plants prepare starch from carbon dioxide and water in the presence of sunlight by the process of photosynthesis. This reaction is slow in dim sunlight but it is much faster in bright sunlight.
Presence of Catalyst
A catalyst is a substance which is added to a reaction mixture to alter the rate of chemical reaction where the mass and the chemical composition of the catalyst remain unchanged at the end of the reaction. Many industrially important reactions such as manufacture of ammonia, sulphuric acid, nitric acid and polythene are carried out using suitable catalysts.
Chemical Equilibrium
In reversible chemical reactions, there is a point when forward and backward reactions proceed simultaneously at the same rate. This is called Chemical Equilibrium. For instance when hydrogen and iodine are taken in a closed vessel maintained at 717 K, hydrogen molecule combines with iodine molecule to form hydrogen iodide.
H2(g) + I2(g) ←→ 2HI(g)
Since the reaction is reversible in nature, the molecules of hydrogen iodide formed begin to dissociate to form hydrogen and iodine.