Notes On Rate of a Chemical Reaction - CBSE Class 12 Chemistry
One of the most important aspects of the study of chemical reactions, other than predicting their feasibility and the extent to which they would proceed, is the time taken for their completion, the rate of a chemical reaction. Chemical kinetics is the part of physical chemistry that studies reaction rates and explains why certain reactions are instantaneous and others are not. It also describes the conditions in which reaction rates can be altered. In chemical kinetics, the rate of chemical reaction is defined as the rate of decrease in the concentration of one of the reactants (or) the rate of increase in the concentration of one of the products. Thus, the change in the concentration of the reactants or products with respect to time is called the rate of a reaction. Ex: Consider the reaction A → B The rate of reaction is always taken as the change in the concentration of reactants (or) products in a definite interval of time. This is called the average rate of a chemical reaction. rav = - Δ[A]/Δt = Δ[B]/Δt The average reaction rate doesn't predict the rate of reaction at a particular instant of time. The rate of a reaction determined at a particular instant of time is called the instantaneous reaction rate. The rate of reaction may not be the same with respect to all the reactants and products. It depends upon the stoichiometric coefficients of the reactants and the products in a balanced chemical equation. Rate = -1/m . Δ[A]/Δt = -1/n Δ[B]/Δt = 1/o Δ[C]/Δt = 1/p Δ[D]/Δt If the concentration is in mol / litre, then the unit for rate of reaction is mol / litre.sec.

#### Summary

One of the most important aspects of the study of chemical reactions, other than predicting their feasibility and the extent to which they would proceed, is the time taken for their completion, the rate of a chemical reaction. Chemical kinetics is the part of physical chemistry that studies reaction rates and explains why certain reactions are instantaneous and others are not. It also describes the conditions in which reaction rates can be altered. In chemical kinetics, the rate of chemical reaction is defined as the rate of decrease in the concentration of one of the reactants (or) the rate of increase in the concentration of one of the products. Thus, the change in the concentration of the reactants or products with respect to time is called the rate of a reaction. Ex: Consider the reaction A → B The rate of reaction is always taken as the change in the concentration of reactants (or) products in a definite interval of time. This is called the average rate of a chemical reaction. rav = - Δ[A]/Δt = Δ[B]/Δt The average reaction rate doesn't predict the rate of reaction at a particular instant of time. The rate of a reaction determined at a particular instant of time is called the instantaneous reaction rate. The rate of reaction may not be the same with respect to all the reactants and products. It depends upon the stoichiometric coefficients of the reactants and the products in a balanced chemical equation. Rate = -1/m . Δ[A]/Δt = -1/n Δ[B]/Δt = 1/o Δ[C]/Δt = 1/p Δ[D]/Δt If the concentration is in mol / litre, then the unit for rate of reaction is mol / litre.sec.

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