Chemical Kinetics
The branch of chemistry which deals with the rates of chemical reactions and their mechanism, by which they occur, is called chemical kinetics. The kinetic studies not only help us to determine the rate of reaction but also describe the conditions by which the reaction rates can be altered.
In general, various reactions can be categories into three types depending upon the reaction rates-
1) Very fast reaction:
Some reactions are so rapid that they occur as soon as the reactants are mixed. These reactions involving ionic species are very fast. For example, the precipitation of silver chloride occurs very quickly on mixing the solutions of silver nitrate and sodium chloride.
NaCl + AgNO3 ———> AgCl ↓ + NaNO3
Similarly, the neutralisation of an acid by a base occurs as soon as the two substances are mixed. The rate of reaction cannot be determined easily. The reason for a very fast rate of such reaction is that these reactions involve only the ions. These reactions occur in about 10-12 to 10-16 seconds.
2) Very slow reaction:
On the other hand, there are certain reactions which occur at an extremely slow speed. For example, rusting of iron occurs so slowly.
3) Moderately slow reactions:
There are some reactions which occur in a conveniently measurable time and their rates can be measured easily in the laboratory. For example,
Hydrolysis of an ester in the presence of sodium hydroxide.
CH3COOC2H5 + NaOH ———-> CH3COONa + C2H5OH
These are the reactions, which are focus of attention for study.