There are a number of factors which the rate of a reaction is influence by the following factors:
- Concentration of the reactants
- Temperature of the system
- Nature of the reactants and products
- Presence of a catalyst
- Surface area
- Exposure to radiation
1) Concentration of the reactants:
When a chemical reaction occurs, the reactants change over to products. It is observed that with the passage of time the concentrations of the reactants decrease while that of products increases. At a given temperature, the rate of a reaction is directly proportional to the products of molar concentration of the reactants. For examples,
A + B ——–> Products
Then according to law of mass action,
Rate of reaction (r) α [A] [B]
Or, r = k [A] [B]
Where, k = Proportionality constant, called rate constant. [A] = molar cone. of A [B] = molar cone. of B
2) Temperature of the system:
In general, an increase in the temperature increases the rate of almost all chemical reactions.
3) Nature of reactants and the products:
Rates of reactions are influenced by the nature of reactants and products. For example, the oxidation of nitric oxide to nitrogen peroxide takes place fairly rapidly while oxidation of carbon monoxide to carbon dioxide takes place slowly.
2NO + O2 ———> 2NO2 (fast)
2CO + O2 ———> 2CO2 (slow)
4) Presence of catalyst:
It has been observed that many reactions are made to proceed at an increased rate by the presence of certain catalysts. For example, a mixture of H2 and O2 does not react at room temperature. However, in the presence of a catalyst such as finely divided platinum, the reaction becomes quite vigorous.
5) Exposure of radiation:
In some cases, the rate of a chemical reaction is considerably increased by the use of certain radiations. For example, reaction of hydrogen and chlorine takes place very slowly in the absence of light. However, in the presence of light, the reaction takes place very rapidly.