Shaillee Kaushal is teaching live on Unacademy Plus
XII-04 KINETICS I
Introduction:- , Thermodynamics deals with the feasibility of a chemical change by taking the value of AG to be negative. But even though the value of AG be negative the reactants do not form products instantaneously and actual rate of the reaction may vary from exteremly slow to very fast Thermodynamics only deal with the initial and final states of reacting systems but offers no explanation about the various stages to which the reactants pass to reach the final state. The branch of physical chemistry which deals with the rate at which the chemical reactions occur, the mechanism by which the chemical reactions take place and the influence of various factors such as concentration, temperature, pressure, catalyst etc. on the reaction rates is called the chemical kinetics.
Very fast or instantaneous reactions: These reactions are so fast that they occur as soon as the reactants are brought together. These reactions involve ionic species and thus known as ionic reactions. It is not possible to determine the rates of these reactions For example: (i) AgNO3 +NaCl AgClI +NaNO3 (ii) Bacl2 + H2SO4 BaSO4 +2HC (iii) HCl + NaOHNaCl + H20
Very slow reactions > There are certain reactions which are very slow. It is difficult to study the kinetics of these reactions. For example: (i) 2H2 + 02 2H20 (ii) C + O2 CO2 (iii) Rusting of iron Room temp Room temp
Moderate reactions:- Many reactions take place at moderate and measurable rates at room temperature and kinetics of such reactions can be studied. Mostly these reactions are molecular in nature. For example:- (i) Decomposition of hydrogen peroxide (ii) Decomposition of N205 (ii) Reactions between NO2 and CO
(i) To predict the rate of a particle reactions under specified conditions: By studying the kinetics of the reactions certain conditions can be varied in order to get maximum yields of products in the industries. (ii) To predict mechanism of reactions