Gibbs equation and third law of thermodynamics

[kelvin490]

I have seen a discussion of what would happen for an ideal gas expands irreversibly and adiabatically until absolute zero degree K. The entropy change is like that:

Δs=C_v ln(T₂/T₁)+R ln(V₂/V₁)

It is impossible for T₂ to be zero K in the equation and so it becomes one justification of the third law. I wonder whether it is valid and whether an irreversible process can be represented by the above equation. For irreversible process the heat exchange is not equal to Tds so can the Gibbs equation be applied?

 

[elegysix]

I have seen a discussion of what would happen for an ideal gas expands irreversibly and adiabatically until absolute zero degree K.

This begs the question of whether an average molecule in this ideal gas has more kinetic energy than gravitational potential energy.