Internal heat

[kanikubari]

Why does change internal heat equal work+heat when the change of pressure=0?

[Steven Garcia 1H]

Well depending on the system, energy could still be transferred in the terms of heat and work. Even though the pressure is constant, there’s still an opposing force which work may be required to act against. In regards to heat, heat transfer is usually always present with a change in temp. except in the case of an isolated system.

Hope this helps!

[Angel Chen 2k]

In the constant-pressure process, the gas can still do the work. Also, when it interacts with other systems with different temperatures, heat can be transferred between them (if neither of them is an isolated system). Therefore, since both Q and W can be changed in this process, the internal energy could change.