Question

Given that heats of combustion of ethylene, hydrogen and ethane are -337.0, -68.4 and -373.0 kcal respectively at $25^\circ C$ , the heat of reaction

$C_{2}H_{4}\left(\right.g\left.\right)+H_{2}\left(\right.g\left.\right) \rightarrow C_{2}H_{6}\left(\right.g) \, $ at $25^\circ C$ will be

• A. -32.4 kcal
• B. -36.3 kcal
• C. -37.8 kcal
• D. -39.2 kcal

Answer 1

Answer: (A)

$\Delta H_{r x n}=\Sigma \Delta H_{c}$ (Reactants) $-\Sigma \Delta H_{c}$ (Products)

$= \left(- 337.0 \, \text{kcal} - 68.4 \, \text{kcal}\right) - \left(- 373 \, \text{kcal}\right)$

$=\left(\right.-337.0-68.4+373\left.\right)kcal=-32.4 kcal$ .