Question

Write the expression for the equilibrium constant, K_c for each of the following reactions: 

1. \(2NOCl (g) ⇋ 2NO (g) + Cl_2 (g)\)
2. \(2Cu(NO_3)_2 (s) ⇋ 2CuO (s) + 4NO_2 (g) + O_2 (g)\)
3. \(CH_3COOC_2H_5(aq) + H_2O(l) ⇋ CH_3COOH (aq) + C_2H_5OH (aq)\)
4. \(Fe^{3+} (aq) + 3OH^– (aq) ⇋ Fe(OH)_3 (s)\)
5. \(I_2 (s) + 5F_2 ⇋ 2IF_5\)

Answer 1

Equilibrium constant expressions (K_c):

While writing K_c, only the concentrations of gaseous and aqueous species are included. Pure solids and liquids are omitted.

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(i) 2NOCl (g) ⇋ 2NO (g) + Cl₂ (g)

K_c = [NO]² [Cl₂] / [NOCl]²

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(ii) 2Cu(NO₃)₂ (s) ⇋ 2CuO (s) + 4NO₂ (g) + O₂ (g)

K_c = [NO₂]⁴ [O₂]

(Solids are omitted from the expression.)

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(iii) CH₃COOC₂H₅ (aq) + H₂O (l) ⇋ CH₃COOH (aq) + C₂H₅OH (aq)

K_c = [CH₃COOH][C₂H₅OH] / [CH₃COOC₂H₅]

(Water is omitted as it is a pure liquid.)

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(iv) Fe³⁺ (aq) + 3OH⁻ (aq) ⇋ Fe(OH)₃ (s)

K_c = 1 / ( [Fe³⁺] [OH⁻]³ )

(Solid Fe(OH)₃ is omitted.)

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(v) I₂ (s) + 5F₂ (g) ⇋ 2IF₅ (g)

K_c = [IF₅]² / [F₂]⁵

(Solid iodine is omitted.)

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Conclusion:

Equilibrium constant expressions include only variable concentrations of gaseous and aqueous species, while pure solids and liquids are excluded.