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Equilibrium

Chemical equilibrium, Le Chatelier's principle, acids & bases

Key Concepts
  • Dynamic equilibrium: forward and reverse rates are equal
  • Le Chatelier's principle: system shifts to oppose a change
  • Kc and Kp are related: Kp = Kc(RT)^Δn where Δn = moles of gaseous products − reactants
  • Buffer solution resists pH changes; made from weak acid + its conjugate base
  • Solubility product (Ksp): ion product > Ksp causes precipitation
Important Formulae
Equilibrium constant (Kc) Kc = [products] / [reactants] (coefficients as powers)
Kp from Kc Kp = Kc(RT)^Δn
pH definition pH = −log[H⁺]
Water ionisation Kw = [H⁺][OH⁻] = 10⁻¹⁴ at 25°C
Henderson-Hasselbalch pH = pKa + log([A⁻]/[HA])
Quick Tips
  • Large K (>10³): reaction heavily favours products; small K (<10⁻³): heavily favours reactants.
  • Increasing pressure favours the side with fewer moles of gas.
  • Adding a common ion decreases solubility (common ion effect).
Sample Practice Questions

  1. Degree of dissociation α and Ka for a weak acid HA of concentration c: Ka ≈ :

    • cα
    • cα²
    • c/α
    • α/c
    Show answer

    Answer: cα² (when α << 1)

  2. Addition of catalyst to a system at equilibrium:

    • Shifts equilibrium right
    • Shifts equilibrium left
    • Does not change equilibrium position, only speeds up attainment
    • Changes K
    Show answer

    Answer: Does not change equilibrium position, only speeds up attainment

  3. Bronsted-Lowry acid is defined as a:

    • Proton acceptor
    • Proton donor
    • Electron pair acceptor
    • Electron pair donor
    Show answer

    Answer: Proton donor

  4. For an endothermic reaction, increasing temperature:

    • Decreases K (shifts left)
    • Increases K (shifts right)
    • No effect on K
    • Makes K = 0
    Show answer

    Answer: Increases K (shifts right)

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Practice Questions

Practice 20 randomly selected NEET questions on Equilibrium. Answers are revealed after each question.

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