Thursday, January 31, 2008

JEE Revision - Order of reactions

Rate law

The rate for a reaction is a mathematical expression that relates the rate of reaction to the concentrations of the reactants.

For the reaction aA + bB → products

The rate law is expressed as, rate of reaction is proportional to [A]^x[B]^y.
x and y are determined experimentally. These values can be whole or fractional numbers or zero.

Rate = k[A]^x[B]^y

Order of a reaction

The sum of the powers to which the concentration terms are raised in the rate law expression.

For the expression Rate = k[A]^x[B]^y, the order of the reaction is x+y. The order of the reaction is represented by n.

When n = 1, the reaction said to be first order reaction.
n = 2 second order reaction etc.

There are number of reactions where rate of reaction is independent of concentration of reactants. The order of reaction is zero.

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