Δ H f C 2 H 4=12.5 kcal Heat of atomisation of C =171 kcal Bond energy of H 2=104.3 kcal Bond energy C - H =99.3 kcal What is C=C bond energy?

Question

Δ H f C 2 H 4=12.5 kcal Heat of atomisation of C =171 kcal Bond energy of H 2=104.3 kcal Bond energy C - H =99.3 kcal What is C=C bond energy? (A) 140.9 kcal (B) 49 kcal (C) 40 kcal (D) 76 kcal

Tardigrade Admin · Accepted Answer

Given: 2 C ( text graphite )+2 H 2( g ) longrightarrow C 2 H 4( g ) ; Δ H f Δ H f= Bond dissociation enthalpy of reactant - Bond dissociation enthalpy of products =12.5=(171 × 2)+2 × 104.3-(4 × 99.3+ BE C = C ) ∴ BE ( C = C )=140.9 kcal

Q. $Δ H_{f} C_{2} H_{4} = 12.5 k c a l$
Heat of atomisation of $C = 171 k c a l$
Bond energy of $H_{2} = 104.3 k c a l$
Bond energy $C - H = 99.3 k c a l$
What is $C = C$ bond energy?

140.9 kcal

49 kcal

40 kcal

76 kcal

Given:
$2 C_{(graphite)} + 2 H_{2} (g) ⟶ C_{2} H_{4} (g); Δ H_{f}$
$Δ H_{f} =$ Bond dissociation enthalpy of reactant $-$ Bond dissociation enthalpy of products
$= 12.5 = (171 \times 2) + 2 \times 104.3 - (4 \times 99.3 + B E_{C = C})$
$∴ B E_{(C = C)} = 140.9 k c a l$

Q. ΔHf​C2​H4​=12.5kcal Heat of atomisation of C=171kcal Bond energy of H2​=104.3kcal Bond energy C−H=99.3kcal What is C=C bond energy?