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COMEDK2023Morning ShiftChemistryThermodynamics (C)Actual

If 2 moles of C ₂ H ₆(g) are completely burnt and 4100 kJ of heat is liberated. If H^ for CO ₂(g) and H ₂ O (l) are -410 and -285 kJ per mole respectively, then the heat of formation of C ₂ H ₆(g) is

Options

  1. A-116 ~kJ
  2. B+375 ~kJ
  3. C+775 ~kJ
  4. D-885 ~kJ

Correct answer

B. +375 ~kJ

Step-by-step solution

Combustion of 2 moles of C₂H₆ : 2C₂H₆(g) + 7O₂(g) 4CO₂(g) + 6H₂O(l) , H_ rxn = -4100 kJ H_ rxn = [4 H_f^0(CO₂) + 6 H_f^0(H₂O)] - [2 H_f^0(C₂H₆)] -4100 = [4(-410) + 6(-285)] - 2 H_f^0(C₂H₆) -4100 = [-1640 - 1710] - 2 H_f^0(C₂H₆) -4100 = -3350 - 2 H_f^0(C₂H₆) 2 H_f^0(C₂H₆) = -3350 + 4100 = 750 H_f^0(C₂H₆) = +375 kJ/mol

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