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BITSAT2018ChemistryThermodynamics (C)Actual

Enthalpy of combustion of methane and ethane are - 210 k cal / mol and - 368 k cal / mol respectively. The enthalpy of combustion of decane is

Options

  1. A- 1582   kcal
  2. B- 1632   kcal
  3. C- 1700   kcal
  4. D- 1480   kcal

Correct answer

B. - 1632   kcal

Step-by-step solution

Given, CH 4 + 2 O 2 ⟶ CO 2 + 2 H 2 O ;   ΔH = - 210   kcal / mol . . . ( i ) C 2 H 6 + 7 2 O 2 ⟶ 2 CO 2 + 3 H 2 O ;   ΔH = - 368   kcal / mol . . . ( ii ) On subtracting Eq. ( i ) from Eq ( ii ) , we get CH 2 + 3 2 O 2 ⟶ CO 2 + H 2 O ;   ΔH = - 158   kcal / mol ∴ Enthalpy of combustion of one CH 2   unit = - 158   kcal / mol ΔH comb C 10 H 22 = ΔH comb CH 4 + 9 × ΔH comb CH 2 = - 210 + 9 × - 158 = - 1632 &#160

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