How does the internal energy of a given mass of gas depends upon Pressure, Volume, Temperature of gas, Process in achieving that state of mass of gas?
Pressure: If the pressure falls but the temp doesnt change then there is no change in the internal energy of a system.
Volume: The internal energy of an ideal gas depends only on the temperature of the gas, and is independent of the volume. This is pretty obvious, since if there are no interatomic forces then increasing the volume, which effectively increases the mean separation between molecules, is not going to affect the molecular energies in any way. Hence, the energy of the whole gas is unaffected.
State: For most materials that change from solid to liquid the volume increases and so the potential energy of the molecules increases.