Chapter 3: Chemical KineticsClass 12 Chemistry — summary, notes, extra questions & MCQ quiz

Summary

Chemical kinetics deals with the rates of reactions, the factors that control them and the mechanisms by which they occur. The rate of a reaction is the change in concentration of a reactant or product per unit time, expressed as average or instantaneous rate. The rate depends on concentration through the rate law, \(\text{rate}=k[A]^x[B]^y\), where the exponents give the order with respect to each reactant and their sum is the overall order; \(k\) is the rate constant. Order is determined experimentally and may differ from the stoichiometric coefficients, while molecularity refers to the number of species in an elementary step. Integrated rate equations give concentration as a function of time: zero order reactions have rate independent of concentration, and first order reactions follow \(k=\dfrac{2.303}{t}\log\dfrac{[A]_0}{[A]}\) with a constant half-life. Temperature strongly affects rate; the Arrhenius equation \(k=Ae^{-E_a/RT}\) links the rate constant to the activation energy \(E_a\) and temperature. According to collision theory, only molecules colliding with sufficient energy and proper orientation react, and a catalyst speeds up a reaction by providing an alternative path of lower activation energy without being consumed.

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