For an ideal gas at fixed temperature and pressure, the total energy remains constant regardless of the size of the system. This behavior is based on the ideal gas law, which states that for an ideal gas:
PV = nRT
Where: P is the pressure V is the volume n is the number of moles of gas R is the ideal gas constant T is the temperature
If we consider a fixed temperature and pressure, the equation can be rearranged as:
V = (nRT)/P
From this equation, it becomes clear that the volume (V) of the gas is inversely proportional to the pressure (P). As the size of the system changes, the volume will adjust accordingly to maintain the fixed pressure and temperature. However, the product of the pressure and volume, which represents the total energy of the gas, remains constant.
In summary, for an ideal gas at fixed temperature and pressure, the total energy of the system does not change with the increasing or decreasing size of the system.