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Chemical Equilibrium question

2024 · 31 Jan · Shift 1 · Q12
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  5. /2024 · 31 Jan · Shift 1 · Q12

Chemical Equilibrium question

2024 · 31 Jan · Shift 1 · Q12

JEE MainChemistryChemical EquilibriumMCQ+4 / −1
For the given reaction, choose the correct expression of KC\mathrm{K}_{\mathrm{C}}KC​ from the following :-Fe(aq)3++SCN(aq)−⇌(FeSCN)(aq)2+\mathrm{Fe}_{(\mathrm{aq})}^{3+}+\mathrm{SCN}_{(\mathrm{aq})}^{-} \rightleftharpoons(\mathrm{FeSCN})_{(\mathrm{aq})}^{2+}Fe(aq)3+​+SCN(aq)−​⇌(FeSCN)(aq)2+​
  1. A
    KC=[Fe3+][SCN−][FeSCN2+]\mathrm{K}_{\mathrm{C}}=\frac{\left[\mathrm{Fe}^{3+}\right]\left[\mathrm{SCN}^{-}\right]}{\left[\mathrm{FeSCN}^{2+}\right]}KC​=[FeSCN2+][Fe3+][SCN−]​
  2. B
    KC=[FeSCN2+][Fe3+][SCN−]\mathrm{K}_{\mathrm{C}}=\frac{\left[\mathrm{FeSCN}^{2+}\right]}{\left[\mathrm{Fe}^{3+}\right]\left[\mathrm{SCN}^{-}\right]}KC​=[Fe3+][SCN−][FeSCN2+]​
  3. C
    KC=[FeSCN2+]2[Fe3+][SCN−]\mathrm{K}_{\mathrm{C}}=\frac{\left[\mathrm{FeSCN}^{2+}\right]^2}{\left[\mathrm{Fe}^{3+}\right]\left[\mathrm{SCN}^{-}\right]}KC​=[Fe3+][SCN−][FeSCN2+]2​
  4. D
    KC=[FeSCN2+][Fe3+]2[SCN−]2\mathrm{K}_{\mathrm{C}}=\frac{\left[\mathrm{FeSCN}^{2+}\right]}{\left[\mathrm{Fe}^{3+}\right]^2\left[\mathrm{SCN}^{-}\right]^2}KC​=[Fe3+]2[SCN−]2[FeSCN2+]​
View written solutionFree

Correct answer: B

  1. Write the balanced equilibrium reaction

Fe(aq)3++SCN(aq)−⇌FeSCN(aq)2+\mathrm{Fe}^{3+}_{(aq)} + \mathrm{SCN}^{-}_{(aq)} \rightleftharpoons \mathrm{FeSCN}^{2+}_{(aq)}Fe(aq)3+​+SCN(aq)−​⇌FeSCN(aq)2+​

  1. Use the law of mass action

For a general reaction

aA+bB⇌cCaA + bB \rightleftharpoons cCaA+bB⇌cC

we write

KC=[C]c[A]a[B]bK_C = \frac{[C]^c}{[A]^a[B]^b}KC​=[A]a[B]b[C]c​

  1. Identify stoichiometric coefficients

Here, all coefficients are 111:

  • Fe3+\mathrm{Fe}^{3+}Fe3+ : 111
  • SCN−\mathrm{SCN}^{-}SCN− : 111
  • FeSCN2+\mathrm{FeSCN}^{2+}FeSCN2+ : 111

So,

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

  1. Compare with the given options
  • A: Inverted expression, so incorrect.
  • B: [FeSCN2+][Fe3+][SCN−]\frac{[\mathrm{FeSCN}^{2+}]}{[\mathrm{Fe}^{3+}][\mathrm{SCN}^{-}]}[Fe3+][SCN−][FeSCN2+]​ correct.
  • C: Product concentration wrongly squared, incorrect.
  • D: Reactant concentrations wrongly squared, incorrect.

Therefore, the correct option is B.

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