Suppose we had an isolated, isovolumetric system in which the reaction
$${N_2 + 2H_2 \to 2NH_3}$$
Takes place. If we had to determine the signs of heat, work, change in internal energy and change in enthalpy, this would be my approach but I don't know if it makes sense.
It is an isolated system, so $Q=W= \Delta U = 0$
$\text{Change in enthalpy}=\Delta U+\Delta (pV) = V\Delta (p)$
Since the number of moles is decreasing, the pressure must decrease as well considering there is no volume change meaning $\Delta H$ is negative.
I also don't know if temperature is constant or if it is changing because I thought enthalpy was a function of temperature as well.
I'm having a hard time grasping how change in internal energy can be zero and how change in enthalpy is negative. I also don't know if my reasoning is correct.
Thank you.