JEE Main & Advanced Chemistry Chemical Kinetics Factors Affecting Rate Of A Reaction

Factors Affecting Rate Of A Reaction

Category : JEE Main & Advanced

The rate of a chemical reaction depends on the following things

(1) Nature of reactants

(i) Physical state of reactants : This has considerable effect over rate of reaction.

\[\underset{\text{Decreasing rate of reaction}}{\mathop{\xrightarrow{\text{Gaseous satae }>\text{Liquid state}>\text{Solid state}}}}\,\]

(ii) Physical size of the reactants : Among the solids, rate increases with decrease in particle size of the solid.

(iii) Chemical nature of the reactants

(a) Reactions involving polar and ionic substances including the proton transfer reactions are usually very fast. On the other hand, the reaction in which bonds is rearranged, or electrons transferred are slow.

(b) Oxidation-reduction reactions, which involve transfer of electrons, are also slow as compared to the ionic substance.

(c) Substitution reactions are relatively much slower.

(2) Effect of temperature : The rate of chemical reaction generally increases on increasing the temperature. The rate of a reaction becomes almost double or tripled for every \[{{10}^{o}}C\] rise in temperature.

Temperature coefficient of a reaction is defined as the ratio of rate constants at two temperatures differing by (generally 25°C and 35°C) 10°C.

\[\mu =\]\[\text{Temperature coefficient}=\frac{k\,\text{at (t}+\text{1}{{\text{0}}^{\text{o}}}C)}{k\,\text{at }{{t}^{o}}C}=\frac{{{k}_{{{35}^{o}}C}}}{{{k}_{{{25}^{o}}C}}}\]

 (3) Concentration of reactants : The rate of a chemical reaction is directly proportional to the concentration of the reactants means rate of reaction decreases with decrease in concentration.

(4) Presence of catalyst : The function of a catalyst is to lower down the activation energy. The greater the decrease in the activation energy caused by the catalyst, higher will be the reaction rate.


(5) Effect of sunlight :  There are many chemical reactions whose rate are influenced by radiations particularly by ultraviolet and visible light. Such reactions are called photochemical reactions. For example, Photosynthesis, Photography, Blue printing, Photochemical synthesis of compounds etc.

The radiant energy initiates the chemical reaction by supplying the necessary activation energy required for the reaction.

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