Equilibrium — Class 11 Chemistry

This unit develops the idea of equilibrium for both physical and chemical systems. Physical equilibria — solid-liquid, liquid-vapour, solid-vapour and the dissolution of solids and gases in liquids (Henry's law) — are dynamic, with opposing processes proceeding at equal rates in a closed system so that measurable properties stay constant. Chemical equilibrium is likewise dynamic, demonstrated by the Haber synthesis of ammonia and by isotope-scrambling experiments. The law of chemical equilibrium (the law of mass action of Guldberg and Waage) gives the equilibrium constant as the ratio of product to reactant concentrations each raised to its stoichiometric coefficient. For gaseous reactions is used, with ; pure solids and liquids are omitted from heterogeneous equilibrium constants. The magnitude of indicates the extent of a reaction, while the reaction quotient predicts the direction of net change. Equilibrium connects to thermodynamics through . Le Chatelier's principle explains how concentration, pressure, temperature and catalysts affect equilibrium, a catalyst speeding both directions equally without shifting the position. The unit then turns to ionic equilibrium: strong and weak electrolytes; the Arrhenius, Brønsted-Lowry (conjugate acid-base pairs) and Lewis concepts of acids and bases; ionisation of acids and bases; the ionic product of water , the pH scale, buffer solutions and solubility product.