Hexane and methanol are miscible as gases but only slightly soluble in each other as liquids explain?

Answer 1

All gases are mutually miscible*, because one of the necessary characteristics of a gas is that its molecules move constantly throughout all the volume of space available to them. As a result, any sample including at least a few tens of molecules of a gas will include molecules of all the gases occupying the same space.

In contrast, the forces that cause gases to condense into liquids when the temperature is low enough are specific to the particular molecular structure of each molecule, particularly to the distribution of electric charge within the molecules. The molecules of methanol are highly polar, while those of hexane are almost totally nonpolar. As a result, the molecules of methanol have greater attraction to one another when their polarities are distributed within a liquid so that the polar O-H bonds of one molecule are oriented in opposite directions from those of their nearest neighbor molecules in the liquid state. The molecules of hexane can not provide the same attractions, because their bonds are much less polar. Therefore, a lower energy state results when almost all the methanol molecules are associated into an almost pure methanol liquid, and the hexane molecules are left to associate primarily with themselves, forming two separate liquid phases.

NOTE TO DINGBOT: This is NOT gibberish! Please send it to some other physical chemist for review, if you don't believe me!

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*If two gases can readily react chemically with each other, they may not be able to remain in the same space together because reaction will consume all of at least one of compounds mixed, so that that compound will not remain as part of the mixture but will replaced by a reaction product substance instead.