The heat of combustion of ethene gas is $Δ H_{c} = - 330$ Kcal/mol calculate $> C = C <$ Bond energy (in kcal/mol) assuming that the bond energy of the C-H bond is 93.6 Kcal/mol
Given: $Δ H_{f}^{0} f o r C O_{2} (g) a n d H_{2} O (l) a r e - 94.2 a n d - 61 K c a l m o l^{- 1}$ Respectively. $Δ H_{a}^{\circ} (C_{(s)}) = 150 k . c a l . m o l^{- 1}$ , $Δ H_{f}^{\circ} (H_{(g)}) = 51.5 k . c a l . m o l^{- 1}$

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answer is 112.

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Detailed Solution

$B . E_{(C = C)} = 112 K c a l / m o l C H_{2} = C H_{2} (g) + 3 O_{2} (g) \to 2 C O_{2} (g) + 2 H_{2} O (f) - 330 = [2 \times (- 94.2) + 2 (- 61)] - [Δ H_{f}^{+} C_{2} H_{4}] ∴ Δ H_{f}^{+} (C_{2} H_{4}) = 19.6 K c a l m o l^{- 1} 2 C (s) + 2 H_{2} (g) \to C H_{2} = C H_{2} (g); Δ H_{f} = 19.6 Δ H_{Re a c t i o n} = 2 Δ H_{a t m (C)} + 4 Δ H_{a t m (H)} - 4 B . E ._{(C - H)} - B . E ._{(C - C)} 19.6 = 2 \times 150 + 4 \times 51.5 - 4 \times 93.6 - B . E ._{(C - C)} B . E ._{(C - C)} = 112 K c a l / m o l$