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ExamsNEETChemistry

Let B.E of X1, Y2 and XY are x kJ mol⁻¹, 0.5 x kJ mol⁻¹ and x kJ mol⁻¹ respectively. 1/2 X1 + 1/2 Y2 → XY; ΔH = −200 kJ mol⁻¹. Calculate ΔH.

  1. (a) ΔH = −200 − Σ (B.E)reactants − Σ (B.E)product
  2. (b) ΔH = −200 − Σ (B.E)reactants + Σ (B.E)product
  3. (c) ΔH = −200 + Σ (B.E)reactants − Σ (B.E)product
  4. (d) ΔH = −200 + Σ (B.E)reactants + Σ (B.E)product

Correct answer: (c) ΔH = −200 + Σ (B.E)reactants − Σ (B.E)product

Solution

The enthalpy change (ΔH) is calculated as the sum of bond energies of reactants minus the sum of bond energies of products. Since ΔH is given as −200 kJ mol⁻¹, the correct formula is ΔH = −200 + Σ (B.E)reactants − Σ (B.E)product.

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