Question

What will be the enthalpy of formation of toluene considering the data given? Bond energies of $ C — C = 79 \,kcal, C = C = 135 \,kcal, C — H = 102 \,kcal $ , heat of atomisation of $ C = 156.8\, kcal $ and heat of atomisation of $ H = 49.5 \,kcal $

• A. $ -43.4 \,kcal $
• B. $ 43.4 \,kcal $
• C. $ 114.6 \,kcal $
• D. $ -114.6 \,kcal $

Answer 1

Answer: (A)

$7C_{\left(g\right)}+4H_{2\left(g\right)} \rightarrow\underset{\text{Toluene}}{{C_{7}H_{8(g)}}}$
$\Delta\,H$ = Enthalpy of atomisation-Bond enthalpies
$=(7\times 156.8+8\times 49.5)-(8\times 102+4\times 79+3\times 135)$
$=1493.6-1537$
$=-43.4$ kcal