In general, chemical reactions are either reversible or irreversible. The concept of a state of equilibrium for the majority of reversible reactions is fundamental in chemistry. Students should appreciate the dynamic nature of chemical equilibrium, in particular the shifting of equilibrium position when a system at equilibrium is subjected to a change. It is therefore important to control variables such as pressure, concentration and temperature in an industrial process so as to establish the optimal reaction conditions. A more in depth treatment of the above concepts is included in Topic XIII “Industrial Chemistry”.

The equilibrium law provides a quantitative relationship between the concentrations of the reactants and products in systems which are existing in a state of equilibrium. Students should understand the equilibrium constant K c and its mathematical treatment in relation to the stoichiometry of reactions. Students should also be able to predict the effect of changes in either concentration or temperature on the position of chemical equilibrium in a homogeneous reaction. But the effect on the position of equilibrium of introducing species not involved in the chemical reaction is not required. Detailed treatment of equilibrium systems involving redox and acid-base reactions are not expected at this level of study.

 

The concept of chemical equilibrium has a number of applications in daily life. Information search and reading on related topics can help students to build up their understanding of the concepts involved as well as the relationship between different types of equilibria.