# Factors Influencing Rate of Reaction

Some important factors which influence the rate of reaction are given below:

1. Effect of Concentration: As discussed above rate of a reaction decreases with decrease of concentration of the reactants. (Rate $\propto$ concentration).

2. Effect of Temperature: It is observed that rate of a reaction increases with rise of temperature. In general rate of a reaction becomes double on rise of $10^0C$ (usually $25^0 -35^0C$).

3. Effect of the Nature of Reactants: It is observed that the reactions in which simple ions are involved; take place faster than the reactions in which ions of considerable bonds are involved. For example, oxidation of $Fe^{2+}$ ion by permanganate ion $(MnO^-_4$ ion) in acidic medium takes place faster than the oxidation of $C_2O^{2-}_4$ ion under same conditions.

$5Fe^{2+} + MnO^-_4 + 8H \to 5Fe^{3+} + Mn^{2+} + 4H_2O$ (faster)

$5C_2O^{2-}_4 + 2MnO^-_4 + 16H^+ \to 10CO_2 + Mn^{2+} + 8H_2O$ (slow)

In the same way oxidation of NO takes place faster than $CH_4$.

$2NO + O_2 \to 2NO_2$ (faster)

$CH_4 + 2O_2 \to CO_2 + 2H_2O$ (slow)

4. Effect of Catalyst: In general catalyst increases the rate of reaction. Actually catalysts form new path of the chemical reaction of low activation energy.

5. Effect of Surface Area of Reactants: It is observed that the smaller particles react more rapidly than the larger particles of same mass. For example coal dust burns rapidly than that of large lumps of coal. Smaller chips of wood bum more rapidly than a log of wood of the same mass.

6. Effect of Radiation: Rate of certain reactions increases the absorption of photons of certain radiations. Such reactions are known as photochemical reactions.

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