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Cheat sheet · Class 11 · CBSE · Science Chemistry

Equilibrium cheat sheet

The whole chapter on one page: key formulas, facts and the points to remember, for quick revision before a test.

CBSE Class 11 · Chemistry

Cheat sheet

Chapter 6Equilibrium

Le Chatelier: a system shifts to undo the change you make.

1. Equilibrium Constants

For aA+bB⇌cC+dDaA + bB \rightleftharpoons cC + dD:

Kc=[C]c[D]d[A]a[B]bK_c = \dfrac{[C]^c[D]^d}{[A]^a[B]^b}
Kp=Kc(RT)ΔnK_p = K_c(RT)^{\Delta n}

Compare QQ with KK: Q < K → forward; Q > K → backward; Q = K → equilibrium.

2. Le Chatelier's Principle

ChangeShift
Add reactantforward
Increase pressureside with fewer gas moles
Raise T (exothermic)backward; K decreases
Catalystno shift; equilibrium reached faster

3. Ionic Equilibrium

Kw=[H+][OH−]=10−14K_w = [H^+][OH^-] = 10^{-14} at 298 K
pH=−log⁡[H+]pH = -\log[H^+]pH+pOH=14pH + pOH = 14
α=KaC\alpha = \sqrt{\dfrac{K_a}{C}} (Ostwald)[H+]=KaC[H^+] = \sqrt{K_aC}
  • Arrhenius, Brønsted–Lowry (proton donor/acceptor), Lewis (electron-pair acceptor/donor).
  • Conjugate pair: K_a × K_b = K_w.

4. Buffers

pH=pKa+log⁡[salt][acid]pH = pK_a + \log\dfrac{[\text{salt}]}{[\text{acid}]}

Henderson–Hasselbalch equation; acidic buffer CH₃COOH/CH₃COONa.

5. Solubility Product

For AxByA_xB_y: Ksp=(xs)x(ys)yK_{sp} = (xs)^x(ys)^y.

  • Precipitation when ionic product > K_sp.
  • Common ion effect lowers solubility.

6. Key Points

  • K depends only on temperature.
  • Pure solids/liquids are left out of K.
  • Salt of strong acid + weak base is acidic.
  • Equilibrium is dynamic.

Remember: K_c, K_p | Le Chatelier | pH, K_a, buffers | K_sp

Equilibrium: questions and notes

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