In one of my previous questions, I got an answer from user Jan:

The smell of a compound as we perceive it usually depends on which receptors in the nose will bind the molecule (or not).

These receptor, being proteins, are usually rather specific for certain shapes, not for bonding patterns. So chlorobenzene might fit into similar receptors as toluene which would lead to at least partly a similar smell, but that is it.

This means that a substance must be in the vapour phase in order to smell it, which brings me to my question:

  • Do all substance (at least those which have a characteristic smell) maintain an equilibrium with their vapours (if the substance is in closed container)?

But if it's true for those solids, then it must be true for all other solids, as well as nonvolatile liquids that do not have a characteristic smell to humans. Is this not the case? Also, if this substance is placed in open air, will it evaporate totally?

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    $\begingroup$ You can maintain equilibrium only if vapour is contained. $\endgroup$
    – Mithoron
    Commented Oct 23, 2015 at 19:19
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    $\begingroup$ The solid or liquid is at equilibrium with its vapor at the air interface. But, typically, the partial pressure of the substance in the bulk room air will be less than the equilibrium vapor pressure at the interface (except, as Mithoron points out, if the room is sealed). As the substance diffuses from the interface into the bulk room air, its partial pressure decreases with distance from the interface. The pressure gradient provides the driving force for the diffusion. $\endgroup$ Commented Oct 23, 2015 at 20:13
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    $\begingroup$ Yes, everything is partly vapourised, even high-boiling (or -subliming) solids. Equilibrium can, of course, only be reached if the air does not exchange. So put a smelly cheese in your fridge and come back two days later; the smelly cheese will be at vapour pressure equilibrium with the fridge air. Remove the cheese but keep the door closed and the smell will stay for a while. $\endgroup$
    – Jan
    Commented Oct 26, 2015 at 14:29

1 Answer 1


If they were maintaining an equilibrium with their vapour you wouldn't be smelling it.

In theory any equilibrium in the case of vapor pressure occurs in a closed container, in reality a vapor pressure equilibrium is rarely if ever reached.


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