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Thermodynamics question

2002 · Q116
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Thermodynamics question

2002 · Q116

NEETChemistryThermodynamicsMCQ+4 / −1
Heat of combustion Δ\DeltaΔHo for C(s), H2(g) and CH4(g) are −-− 94, −-− 68 and −-−213 kcal/mol, then Δ\DeltaΔHo for C(s) + 2H2(g) →\to→ CH4(g) is
  1. A
    −-−17 kcal
  2. B
    −-−111 kcal
  3. C
    −-−170 kcal
  4. D
    −-−85 kcal
View written solutionFree

Correct answer: A

C(s) + 2H2(g) →\to→ CH4(g), Δ\Delta ΔHo = ?

C(s)

  • O2(g) → CO2(g), Δ\Delta ΔH = – 94 kcal/mol ....(1)

    H2(g) + 12{1 \over 2}21​O2(g) →\to→ H2O(g), Δ\Delta ΔH = – 68 kcal/mol ....(2)

    CH4(g)
  • 2O2(g) →\to→ CO2(g) + H2O(l), Δ\Delta ΔH = – 213 kcal/mol ....(3)

    Performing (1) + 2 × (2) – (3)

    Δ\Delta ΔHo = [– 94 – 2(68)] – (–213) kcal/mol

    = [– 94 – 136] + 213 k cal/mol

    = – 230 + 213 = – 17 kcal/mol
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