When an ideal gas undergoes unrestrained expansion, no cooling occurs because the molecules
a)	Are above the inversion temperature	b)	Exert no attractive forces on each other
c)	Do work equal to loss in kinetic energy	d)	Collide without losing energy

(b)

When a non-ideal gas suddenly expands from a high pressure to a low pressure, there is a temperature change. This is called Joule-Thomson effect. It is an adiabatic effect. The temperature of a real gas is either decreased or increased by letting the gas expand freely at constant enthalpy. When a real gas expands freely at constant enthalpy, the temperature may either decrease or increase, depending on the initial temperature and pressure. For any given pressure, a real gas has an inversion temperature above which the expansion at constant enthalpy causes the temperature to rise, and below which the expansion at constant enthalpy causes cooling. For most gases at atmospheric pressure, the inversion temperature is fairly high (above room temperature), and so most gases at those temperature and pressure conditions are cooled by is isenthalpic expansion. For an ideal gas, there are no intermolecular forces, so no temperature change is expected when the distance between the molecules changes