NEET Chemistry Notes Chemical Kinetics – Concept of Chemical Kinetics
Concept of Chemical Kinetics
Concept of Chemical Kinetics
Chemical kinetics is the branch of chemistry which addresses the rate of chemical reaction. It includes the investigations of how different experimental conditions can influence the speed of a chemical reaction and yield information about the reaction mechanism and transition rates.
Rate of a Reaction
The rate or speed or velocity of a reaction is the rate of change of concentration of reactants or products in unit time.
A → B
Rate of reaction can be defined in two ways:
Factors Affecting the Rate of a Reaction
The rate of chemical reaction depends upon the number of factors such as
- Concentration
- Nature of reactants
- Temperature
- Presence of catalyst
- Exposure to radiations
- Surface area of reactant
Rate Constant and Rate Law
According to law of mass action, the rate of a , chemical reaction is directly proportional to the product of effective concentrations of reacting species, each raised to a suitable power may or may not be equal to the respective stoichiometric coefficients. For a general reaction,
where, k is rate constant or velocity constant or specific reaction rate.
The above expression is called rate law as it describes the functional dependence of the reaction rate upon concentration of various reactants. Rate law cannot be deduced from balanced equation. It is obtained experimentally.
Molecularity
It is defined as the number of ions or molecules or atoms taking part in an elementary process of the reaction mechanism.
In case of simple reactions, known as elementary reactions, the molecularity is simply the sum of molecules of different reactants as represented by balanced equation,
e.g.
In case of complex reactions, i.e. the reactions involving more than one step, the rate determining step is slowest step.
The atoms, molecules or ions participating in this step decide the molecularity
Hence, two molecules participate in slowest step, the reaction is of bimolecular type.