From the following data:
(i) H₂(g) + CO₂(g) ⇌ H₂O(g) + CO(g); K₂₀₀₀ ₖ = 4.4
(ii) 2H₂O(g) ⇌ 2H₂(g) + O₂(g); K₂₀₀₀ ₖ = 5.31 × 10⁻¹⁰
(iii) 2CO(g) + O₂(g) ⇌ 2CO₂(g); K₁₀₀₀ ₖ = 2.24 × 10²²
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Question

From the following data:
(i) H₂(g) + CO₂(g) ⇌ H₂O(g) + CO(g); K₂₀₀₀ ₖ = 4.4
(ii) 2H₂O(g) ⇌ 2H₂(g) + O₂(g); K₂₀₀₀ ₖ = 5.31 × 10⁻¹⁰
(iii) 2CO(g) + O₂(g) ⇌ 2CO₂(g); K₁₀₀₀ ₖ = 2.24 × 10²²
Show whether the reaction (iii) is exothermic or endothermic or thermal?

Prashant Kotian · Accepted Answer

Correct answer: A. First construct reaction (iii) at 2000 K using (i) and (ii): Reversing (ii) gives 2H₂ + O₂ ⇌ 2H₂O (K = 1/K_ii = 1.88×10⁹). Reversing (i) and doubling gives 2H₂O + 2CO ⇌ 2H₂ + 2CO₂ (K = 1/K_i² = 0.051). Adding them gives 2CO + O₂ ⇌ 2CO₂ at 2000 K with K = 1.88×10⁹ × 0.051 ≈ 10⁸. At 1000 K, K is given as 2.24×10²². Since K is much higher at the lower temperature, the reaction must be exothermic. Therefore, correct answer is A.

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