CHEMICAL KINETICS

#. CHEMICAL KINETICS :

It is the branch of chemistry which deals with the study of rates (or fastness) of chemical reactions, the factors affecting it and the mechanism by which the reactions proceed.

• Rate of reaction is the change in concentration of reactants or products per unit time.
For a general reaction,

                                                   A + B -> C
The rate of reaction

The negative sign indicates that the concentration is decreasing with time.
Unit for reaction rate is mol L^-1s^-1.

• The rate of reaction is not a constant quantity (except for zero order reactions). It decreases as the reaction proceeds in the forward direction.

• A rate law expresses a mathematical relationship between the reaction rate and the molar concentration of one or more reactants.

Where m and n are determined experimentally and represent the order of reaction with respect to A and B respectively, m + n represents the overall order of reaction.

• Rate constant is the rate of reaction when the concentration of each of reacting species is unity. It is represented by ‘k’ It is also called specific reaction rate or velocity constant of reaction.

• Order of reaction is defined as the sum of the exponents to which the concentration terms are raised in the rate equation (or rate law) of the reaction. It can be fraction, zero or any whole number.

• Modularity of reaction is defined as the number of reacting particles (atoms or molecules or any other species), which collides simultaneously to bring about the chemical change.
It is a theoretical concept. Its value is always a whole number. It is never more than three. It cannot be zero.