NCERT Solutions for Class 11 Chemistry Chapter 6 Equilibrium

Short Note:

• Equilibrium State: A state in a reversible reaction where the rate of the forward reaction equals the rate of the reverse reaction, making the concentrations of reactants and products constant over time.

• Dynamic Nature of Equilibrium: Reactions do not stop at equilibrium; instead, both forward and backward reactions continue at equal speeds.

• Physical Equilibrium Examples:

  - Solid-Liquid: Ice ⇌ Water at 0°C.

  - Liquid-Vapor: Water ⇌ Water Vapor in a sealed container.

  - Solid-Vapor: Iodine (s) ⇌ Iodine (v).

Short Note:

• Law of Chemical Equilibrium: For a reversible reaction aA + bB ⇌ cC + dD, the equilibrium expression is:

  - In terms of concentration: K_c = [C]^c[D]^d / ([A]^a[B]^b).

  - In terms of partial pressure: K_p = (P_C^c · P_D^d) / (P_A^a · P_B^b).

• Relationship between K_p and K_c:

  - K_p = K_c (RT)^Δn_g, where Δn_g = (moles of gaseous products) - (moles of gaseous reactants).

• Properties of K:

  - If a reaction is reversed, the new equilibrium constant is K' = 1/K.

  - If a reaction is multiplied by a factor n, the new equilibrium constant becomes K' = Kⁿ.

Short Note:

• Le Chatelier's Principle: If a system at equilibrium is subjected to a change in concentration, pressure, temperature, or volume, the system adjusts itself to counteract the effect of the change.

• Effect of Changes:

  - Concentration: Adding reactant shifts equilibrium forward; adding product shifts it backward.

  - Pressure: Increasing pressure shifts equilibrium toward the side with fewer gaseous moles.

  - Temperature: Increasing temperature favors endothermic reactions (ΔH > 0); decreasing temperature favors exothermic reactions (ΔH < 0).

  - Catalyst: Increases the rates of both forward and reverse reactions equally; does not alter the equilibrium position or value of K.

Short Note:

• Acids and Bases Concepts:

  - Arrhenius: Acids give H⁺ ions; Bases give OH^- ions in aqueous solution.

  - Brønsted-Lowry: Acids are proton (H⁺) donors; Bases are proton acceptors.

  - Lewis: Acids are electron-pair acceptors (e.g., BF₃, AlCl₃); Bases are electron-pair donors (e.g., NH₃, H₂O).

• pH Scale: pH = -log[H⁺] and pOH = -log[OH^-]. At 25°C, pH + pOH = 14.

• Buffer Solutions: Solutions that resist changes in pH upon addition of small amounts of acid or base (e.g., CH₃COOH + CH₃COONa).

• Solubility Product Constant (K_sp): For a sparingly soluble salt A_xB_y(s) ⇌ xA^y+(aq) + yB^x-(aq), K_sp = [A^y+]^x [B^x-]^y.