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The combustion of benzene (l) gives CO2 (g) and H2O (l). Given that heat of combustion of benzene at constant volume is −3263.9 kJ mol−1 at 25°C; heat of combustion of benzene at constant pressure will be: (R = 8.314 J K−1 mol−1)

1. 4152.6
2. −452.46
3. 3260
4. −3267.6

Correct answer: −3267.6

Solution

For C6H6(l) + 7.5 O2(g) -> 6 CO2(g) + 3 H2O(l), dng = 6 - 7.5 = -1.5. dH = dU + dng*RT = -3263.9 + (-1.5)(8.314)(298)/1000 = -3263.9 - 3.72 = -3267.6 kJ/mol.

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