Why is it necessary that all inter-molecular collisions in an ideal gas be elastic?
My understanding is that a gas behaves ideally so long as the potential energy arising from inter-molecular interactions is negligible compared to the kinetic energy. Collisions are necessary to establish equilibrium, but the nature of the collisions seems to me irrelevant.
Further, it seems to me that, following a transfer of heat to the gas, inelastic collisions are necessary in order to properly distribute energy among the internal molecular degrees of freedom (vibration, rotation).