Chemical kinetics
Chemical kinetics is that branch of chemistry which deals with the study of the speeds or the rates of chemical reactions, the factors affecting the rates of the reactions and the mechanism by which the reactions proceed. It concerns itself with the measurement of rates of reactions proceeding under the given conditions of temperature, pressure and concentration.
Chemical Reactions are classified into following on the Basis of Rate of Reaction :- 1. Fast/instantaneous reactions :-It is practically impossible to measure the speed of such reactions, e.g., ionic reactions. organic substitution reactions. 2. Slow reactions Chemical re actions which completes in a long time from some minutes to some years are called slow reactions. e.g., rusting of iron. transformation of diamond etc. 3. Moderately slow reactions Chemical reactions which are intermediate between slow and fast reactions are called moderately slow reactions.
Chemical reaction rates are the rates of change in concentrations or amounts of either reactants or products.The rate of a reaction depends on the concentration of reactants. As the reaction proceeds the reactants get consumed and their concentration decreases with time. Therefore, the rate of reaction does not remain constant during the entire reaction.
Various Factors Affecting Rate of Reaction are:-
- Nature and concentration of reactant :-Generally the rate of a reaction increases as the concentration of the reactants is increased.
- Temperature :-A reaction is faster when the reaction temperature is increased.
- Surface area of reactant
- Radiations and catalyst
- Pressure of gas
- Presence of a Catalyst:-A catalyst alters the reaction rate without being consumed by the reaction.
Rate law is defined as the mathematical relationship between rate of a reaction and the concentration of the reactants.
x y rate = k [A] [B]
Half-life is the time taken for the concentration of a reactant to drop to half its original value. In a first-order chemical reaction, the half-life of the reactant is ln(2)/?, where ? is the reaction rate constant.