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For the reaction C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(l) at 27 °C, the enthalpy change is −1366.5 kJ mol−1. What is the corresponding internal energy change at this temperature?

1. −1369.0 kJ
2. −1364.0 kJ
3. −1361.5 kJ
4. −1371.5 kJ

Correct answer: −1364.0 kJ

Solution

delta n_gas = 2 - 3 = -1. dU = dH - (delta n)RT = -1366.5 - (-1)(8.314e-3 kJ)(300) = -1366.5 + 2.49 = -1364.0 kJ. Correct option: -1364.0 kJ.

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