Question

The enthalpy of combustion of cyclohexane, 1, 4-cyclohexadiene and H₂ are respectively –3920, –3680 and –241 KJ mol^–1. The heat of hydrogenation of 1, 4-cyclohexadiene is:
1. –121 KJ/mol
2. –242 KJ/mol
3. 242 KJ/mol
4. None of these

Answer 1

Correct Answer - Option 2 : –242 KJ/mol

C₆H₈ + 2H₂ ⟶ C₆H₁₂­, DH_r = ?

DH_r = \(\sum \nu \Delta {H_C}\left( R \right)-\sum \nu \Delta {H_C}\left( P \right)\)

n = stoichiometric coefficient

= –3680 + 2 × (–241) – (–3920)

= –242 KJ/mol