Definition :
The study dealing with the rate of chemical and physical reactions and the factors which influence the reaction rate.
Examples of reactions (rate processes) :
- Stability and incompatibility
- Dissolution
- Absorption, distribution and elimination of a drug
- Drug action at the molecular level
Applications of reaction kinetics :
1-prediction of shelf life of drug products
2-prediction of optimum storage conditions
3-prediction of reaction mechanism and factors affecting it
2-prediction of optimum storage conditions
3-prediction of reaction mechanism and factors affecting it
Rate of reaction :
- The velocity or speed of a reaction given by -/+ dC/dt.
- E.g. formation and hydrolysis of ethyl acetate:
- CH3COOH + C2H5OH CH3COOC2H5+ H2O
- Law of mass action: the rate of a chemical reaction is proportional to the product of the molar concentration of reactants each raised to a power equal to the number of molecules of the substance undergoing reaction.
i.e. aA+ bB+ …..= products
The reaction rate = K (A)a(B)b
Reaction order :
- The overall order of a reaction is the sum of the exponent of the concentration terms that enter into the rate expression. The order with respect to each reactant is the exponent of individual conc. Term.
- Zero, first. Second order reactions