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For complete combustion of ethanol, C2H5OH(l)+3O2(g)→2CO2(g)+3H2O(l), the amount of heat produced as measured in bomb calorimeter, is 1364.47 kJ mol−1 at 25°C. Assuming ideality the enthalpy of combustion, ΔcH, for the reaction will be: (R = 8.314 kJ mol−1)

1. −1366.95 kJ mol−1
2. −1361.95 kJ mol−1
3. −1460.95 kJ mol−1
4. −1350.50 kJ mol−1

Correct answer: −1366.95 kJ mol−1

Solution

Bomb calorimeter gives dU = -1364.47 kJ/mol at constant volume. dn_g = 2 - 3 = -1, so dH = dU + dn_g*R*T = -1364.47 + (-1)(0.008314)(298) = -1366.95 kJ/mol.

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