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KVPY2019ChemistryThermodynamics (C)

Given that, the molar combustion enthalpy of benzene, cyclohexane and hydrogen are x ,   y and z , respectively, the molar enthalpy of hydrogenation of benzene to cyclohexane is

Options

  1. Ax - y + z
  2. Bx - y + 3 z
  3. Cy - x + z
  4. Dy - x + 3 z

Correct answer

B. x - y + 3 z

Step-by-step solution

Hydrogenation of benzene is given by C 6 H 6 + 3 H 2 ⟶ C 6 H 12 . . . ( a ) Enthalpies are given for, C 6 H 6 + 15 2 O 2 ⟶ 6 CO 2 + 3 H 2 O ;   ΔH = x . . . ( b ) C 6 H 12 + 9 O 2 ⟶ 6 CO 2 + 6 H 2 O ;   ΔH = y . . . ( c ) H 2 + 1 2 O 2 ⟶ H 2 ;   ΔH = z . . . ( d ) Reaction ( a ) = ( b ) - ( c ) + 3 ( d ) ∴   ΔH of a = x - y + 3 z

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