Revision: Class 11 >> Equilibrium NEET (UG) Equilibrium

1. Reactions which do not go to completion and occur in both directions simultaneously are called reversible reactions.
2. Reversible reactions proceed in both directions. The direction from reactants to products is the forward reaction, whereas the opposite reaction from products to reactants is called the reverse or backward reaction.
3. A reversible reaction is denoted by drawing in between the reactants and product a double arrow, one pointing in the forward direction and other in the reverse direction (⇌). e.g.
   a. \[\ce{H_{2(g)} + I_{2(g)} ⇌ 2HI_{(g)}}\]
   b. \[\ce{CH3COOH_{(aq)} + H2O_{(l)} ⇌ CH3COO^{-}_{ (aq)} + H3O^{+}_{ (aq)}}\]

The pOH of a solution can be defined as the negative logarithm to the base 10, of the molar concentration of OH⁻ ions in solution.

pOH = -log₁₀[OH^-]

The pH of a solution is defined as the negative logarithm to the base 10, of the concentration of H⁺ ions in solution in mol dm^–3.

pH is expressed mathematically as

pH = -log₁₀ [H⁺] or pH = -log₁₀ [H₃O⁺]

pH scale is a scale for measuring the hydrogen ion concentration in a solution.

A solution containing a weak acid and its salts with strong base is called an acidic buffer solution.

A buffer solution is defined as a solution which resists drastic changes in pH when a small amount of strong acid, strong base, or water is added to it.

1. The pH scale (0–14) measures the concentration of H⁺ ions in a solution; values < 7 indicate acids, > 7 indicate bases, and 7 is neutral.
2. A universal indicator shows different colours at different pH levels, helping to determine the strength of an acid or base.
3. Strong acids/bases produce more H⁺ or OH⁻ ions in solution, while weak acids/bases produce fewer ions at the same concentration.