Chemistry is by its very nature concerned with change and chemists would like to know the speed with which new substances are formed from a given set of starting materials. For example what factors would be important in determining how rapidly foods spoil, what determines the rate at which steel rusts and how would we design a rapidly setting material for dental filling.
The area of chemistry concerned with the speeds, or rates, at which reactions occur is called chemical kinetics. When heated in air, steel wool does not burn. It burns vigorously, however, forming Fe2O3 when heated and then placed in pure oxygen. The different behaviours in air and pure oxygen are due to the different concentrations of O2 in the two environments. The concentrations of reactions influence reaction speeds or rates. Other factors which affect rates of chemical reactions include temperature at which the reaction occurs; the presence of catalyst and the surface area of solid or liquid reactant or catalysts. The study of kinetics therefore provides very useful information on how chemical reactions occur or mechanisms. Kinetics knowledge is valuable for the success of an industrial process where it is imperative to select optimum conditions of the reaction involved.
By the end of this unit you should be able to:
- Express the rate of a given reaction in terms of the variation in concentration of a reactant or product substance with time.