NCERT Book Class 12 Chemistry Chapter 3 Chemical Kinetics

Unit

Objectives
3
Chemical Kinetics
After studying this Unit, you will be
able to
· define the average and Chemical Kinetics helps us to understand how chemical reactions
instantaneous rate of a reaction; occur.
· express the rate of a reaction in
terms of change in concentration Chemistry, by its very nature, is concerned with change.
of either of the reactants or
Substances with well defined properties are converted
products with time;
by chemical reactions into other substances with
· distinguish between elementary
different properties. For any chemical reaction, chemists
and complex reactions;
try to find out
· differentiate between the
molecularity and order of a (a) the feasibility of a chemical reaction which can be
reaction; predicted by thermodynamics ( as you know that a
· define rate constant; reaction with DG < 0, at constant temperature and
· discuss the dependence of rate of pressure is feasible);
reactions on concentration, (b) extent to which a reaction will proceed can be
temperature and catalyst; determined from chemical equilibrium;
· derive integrated rate equations (c) speed of a reaction i.e. time taken by a reaction to
for the zero and first order reach equilibrium.
reactions;
Along with feasibility and extent, it is equally
· determine the rate constants for
zeroth and first order reactions;
important to know the rate and the factors controlling
the rate of a chemical reaction for its complete
· describe collision theory.
understanding. For example, which parameters
determine as to how rapidly food gets spoiled? How
to design a rapidly setting material for dental filling?
Or what controls the rate at which fuel burns in an
auto engine? All these questions can be answered by
the branch of chemistry, which deals with the study
of reaction rates and their mechanisms, called
chemical kinetics. The word kinetics is derived from
the Greek word ‘kinesis’ meaning movement.
Thermodynamics tells only about the feasibility of a
reaction whereas chemical kinetics tells about the rate
of a reaction. For example, thermodynamic data
indicate that diamond shall convert to graphite but
in reality the conversion rate is so slow that the change
is not perceptible at all. Therefore, most people think