JEE Main · 2024 · Shift-IeasyCEQ-018

For the given reaction, choose the correct expression of KC: Fe3+(aq) + SCN-(aq) (FeSCN)2+(aq)

Chemical Equilibrium · Class 11 · JEE Main Previous Year Question

Question

For the given reaction, choose the correct expression of KCK_C: Fe(aq)3++SCN(aq)−⇌(FeSCN)(aq)2+\mathrm{Fe^{3+}_{(aq)} + SCN^-_{(aq)} \rightleftharpoons (FeSCN)^{2+}_{(aq)}}

Options
  1. a

    KC=[FeSCN2+][Fe3+][SCN−]K_C = \frac{[\mathrm{FeSCN^{2+}}]}{[\mathrm{Fe^{3+}}][\mathrm{SCN^-}]}

    ✓
  2. b

    KC=[Fe3+][SCN−][FeSCN2+]K_C = \frac{[\mathrm{Fe^{3+}}][\mathrm{SCN^-}]}{[\mathrm{FeSCN^{2+}}]}

  3. c

    KC=[FeSCN2+][Fe3+]2[SCN−]2K_C = \frac{[\mathrm{FeSCN^{2+}}]}{[\mathrm{Fe^{3+}}]^2[\mathrm{SCN^-}]^2}

  4. d

    KC=[FeSCN2+]2[Fe3+][SCN−]K_C = \frac{[\mathrm{FeSCN^{2+}}]^2}{[\mathrm{Fe^{3+}}][\mathrm{SCN^-}]}

Correct Answera

KC=[FeSCN2+][Fe3+][SCN−]K_C = \frac{[\mathrm{FeSCN^{2+}}]}{[\mathrm{Fe^{3+}}][\mathrm{SCN^-}]}

Detailed Solution

Law of Mass Action: KC=[products]stoich. coeff.[reactants]stoich. coeff.K_C = \frac{\text{[products]}^{\text{stoich. coeff.}}}{\text{[reactants]}^{\text{stoich. coeff.}}}

Step 1 — Identify stoichiometry: Fe3++SCN−⇌FeSCN2+\mathrm{Fe^{3+} + SCN^- \rightleftharpoons FeSCN^{2+}} All coefficients = 1.

Step 2 — Write KCK_C: KC=[FeSCN2+][Fe3+][SCN−]K_C = \frac{[\mathrm{FeSCN^{2+}}]}{[\mathrm{Fe^{3+}}][\mathrm{SCN^-}]}

Answer: Option (1)

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