Equilibrium

Equilibrium is the longest chapter in Class 11 Chemistry and the one that pays back the most in JEE and NEET, because it is really two chapters joined together. The first half is chemical equilibrium: what it means for a reaction to be dynamically balanced, how the equilibrium constant is written from a balanced equation, the relation Kp = Kc(RT) raised to Delta n, why pure solids and liquids are left out, how the reaction quotient Q predicts which way a mixture will move, how an ICE table turns initial amounts into equilibrium concentrations, and how Le Chatelier's principle answers every question about concentration, pressure, temperature, inert gas and catalyst. The second half is ionic equilibrium, which is where most marks are won and lost: the three definitions of acids and bases, the ionic product of water and the pH scale, Ka and Kb with Ostwald's dilution law, the relation Ka x Kb = Kw, the common ion effect, the hydrolysis of the four salt types, buffer solutions and the Henderson-Hasselbalch equation, and finally the solubility product and the prediction of precipitation.