Vapor pressure of a substance, in a given temperature, is the pressure exerted the vapor in a system where the gaseous and liquid phases of the pure substance are in equilibrium.
But, if for a temperature where a compound is obligatorily a gas and cannot be condensed into a liquid at any pressure (like a permanent gas at room temperature), is vapor pressure definable?
And if it isn't definable, does this imply that any mixture between the gas and a liquid (the gas being dissolved in the liquid) is obligatorily non-ideal?
I'm saying that because, for a system where the liquid phase is an ideal mixture and the vapor phase is an ideal gas, Raoult's Law is valid for every component for any proportion between the components, and Henry's Law volatility constant (the variant using molar fraction) for any component becomes simply the vapor pressure of that component at a given temperature.
But, if its vapor pressure isn't definable at that temperature, then it can't be equal.
Perhaps the very fact that one compound can be condensed at that temperature while the other cannot already means that their interactions in the liquid phase cannot be possibly similar?