Midterm 2

[106052916]

At constant pressure and temp, why is delta H not equal to delta U for the following reaction?
N2O5(s) -> 2NO2(g) + 1/2O2(g) and delta H for reactants = 109.5 kJ.mol-1 @ 298 K

[Deep Mehta]

This is because delta U for constant temperature and pressure is 0. And there is expansion because gas is a product so work is negative, with more moles of gas on the right than left. Therefore, 109.5 kJ > 0

[405972194]

Since the question states that the reaction is at constant temperature and pressure, then delta U is 0 since there is not change in temperature, there is not change in internal energy. But the question also just gives the delta H value at 298 K so in this case since 109.5 > 0, delta H > delta U