The combustion of one mole of benzene takes place at 298 K and 1 atm. After combustion, CO2(g) and H2O (l) 
are produced and 3267.0 kJ of heat is liberated.
The standard enthalpy of formation, 
fH of benzene is:
(Standard enthalpies of formation of CO
2(g) and H2O (l) are –393.5 kJ mol–1 and – 285.83 kJ mol–1 respectively.)

1. 54. 24 kJ mol–1
2. 48. 51 kJ mol–1
3. 66. 11 kJ mol–1
4. 15. 21 kJ mol–1

Subtopic:  Hess's Law |
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Given
\(\begin{aligned} &\mathrm{{C}_{{(graphite) }}+{O}_{2}({~g})} → \mathrm{{CO}_{2}({~g})} \\ &\mathrm{\Delta_{r} {H}^{\circ}=-393.5 {~kJ} {~mol}^{-1}} \\ &\mathrm{H_{2}(g) + \frac{1}{2} {O}_{2}({~g})} → \mathrm{{H}_{2} {O}({l})} \\ &\mathrm{\Delta_{r} {H}^{\circ}=-285.8 {~kJ} {~mol}^{-1}} \\ &\mathrm{{CO}_{2}({~g})+2 {H}_{2} {O}({l})} → \mathrm{{CH}_{4}({~g})+2 {O}_{2}({~g})} \\ &\mathrm{\Delta_{r} {H}^{\circ}=+890.3 {~kJ} {~mol}^{-1}} \end{aligned}\)

Based on the above thermochemical equations, the value of ΔrH° at 298 K for the reaction
\(\mathrm{C_{(graphite)} + 2 H_{2} (g) → CH_{4} (g)}\) will  be :

1. –74.8 kJ mol–1

2. –144.0 kJ mol–1

3. +74.8 kJ mol–1

4. +144.0 kJ mol–1

Subtopic:  Hess's Law |
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