How do non-sublimable solids exist in equilibrium with vapour?

All substances exist in equilibrium with their vapour, something I learned from Jan's comment. But my question is how does that happen with solids that are non-sublimable, like ice, piece of iron, or, a piece of cotton?

  • $\begingroup$ Actually, ice sublimes quite easily. But cotton or iron have so low vapor pressure that I think it is unmeasurable (iron is non-volatile because of a high crystal lattice energy, and cotton because it is made of very large molecules that are bound strongly together). $\endgroup$
    – vapid
    Commented Jul 8, 2016 at 13:19
  • $\begingroup$ @vapid So could we say that though verys less but iron and cotton both sublime? $\endgroup$
    – Tyto alba
    Commented Jul 8, 2016 at 13:26
  • $\begingroup$ No, I wouldn't say that. I think that even after billion years you wouldn't be able to observe any loss of mass due to sublimation of these substances. So at any reasonable timescale it is safe to say that iron or cotton doesn't sublime. $\endgroup$
    – vapid
    Commented Jul 8, 2016 at 15:08

2 Answers 2


Thermodynamically, even cotton exists in equilibrium with its vapour, even though this is completely silly in any practical sense. The reason is that thermodynamics does not involve time; it may take $10^9$ years, but so what! The equilibrium may only consists of one molecule / km$^3$ but $technically$ its still equilibrium! This is because you can't arbitrarily pick and choose the cases you want thermodynamics to apply to, but you can apply reasonable physical insight based on observation rather than applying theory blindly.

  • $\begingroup$ There is no such thing as 'cotton vapor.' Thermodynamically, cotton fibers decompose. $\endgroup$ Commented Jul 8, 2016 at 18:47
  • $\begingroup$ I agree with porphyrin and disagree with Agriculturist's comment. For a given cellulose chain length in a given crystal structure, there will be some theoretical vapor pressure of that cellulose chain. It might be lower than the "vacuum" of intergalactic space, but there is still some non-zero value. $\endgroup$
    – Curt F.
    Commented Jul 8, 2016 at 20:17
  • $\begingroup$ So a shirt converts to its 'shirt vapor' if thrown into a theoretical vacuum. While this sounds absurd, a shirt is only slightly more complex than a cotton fiber. A living cotton fiber is covered in pectin and other compounds. The inside has a lumen which dies off when the bowl opens. The middle layers contain mostly cellulose with varying chemical properties. This answer needs refinement; for instance, it may make sense to talk about a homogeneous compound like cellulose along with which theory, body of literature, or viewpoint this answer refers. $\endgroup$ Commented Jul 13, 2016 at 21:06

This questions seems based on out-dated theory of olefaction (which is the science of smells.)

In the old theory, the nose detects minute particles of a substance in air by receptors keyed for specific particles. These particles are assumed to be in the air because we can smell them.

This old theory can be refuted based on three observations:

  1. Compounds with different chemical compositions can smell exactly the same. (creosol and eugenol)
  2. Compounds of different isotopes can smell different. (musk)
  3. Concentrations of compounds can change the odor completely. (phenol)

Since the advent of genetic technologies, a new theory is on the horizon is the underlying mechanism for smell is based on quantum oscillations. This theory is derived from information gathered from studying the genome which encodes the proteins responsible for the sense of smell.

The metallic smell does not come from metal. One current theory is the metal causes lipids on the skin to oxidize. The oxidized lipids are what travels to the nose. The nose is actually picking up a human scent of blood at a very small concentration. Even at small concentrations, blood is something the which the nose is extremely sensitive.

  • $\begingroup$ This reply does not answer this question. The idea of molecular vibrations of one type of molecules vs. another causing us to perceive different smells, 'quantum oscillations' as you call them, is still very speculative. I am very surprised that isotopic substitution say H for D, such as in naphthalene (moth ball smell), causes a difference. If it did it would be a plus for a molecular vibration to smell model. I don't think that its true that we are $very sensitive$ to smell of blood, taste maybe, but if I have small cut I don't smell blood. $\endgroup$
    – porphyrin
    Commented Jul 8, 2016 at 17:20
  • $\begingroup$ @porphyrin - The question is based on a premise derived from outdated science which has been recently called into question. The odor detection threshold for blood is typically in the parts per trillion range; however, your threshold could be different based on both your geneotype, phenotype, alleotype, health, and psychological biases. $\endgroup$ Commented Jul 8, 2016 at 18:02
  • $\begingroup$ Looks you wanted to recycle your answer, but it didn't go well. Question is simply about non-zero vapor pressure not smell. $\endgroup$
    – Mithoron
    Commented Jul 8, 2016 at 18:16
  • $\begingroup$ @Mithoron - The question references 'Jan's answer' . The answer to a different question is what created the confusion, so I answered the question here then backtracked to the older answer and included the information there as well. Looks like you were jumping to conclusions without studying the question. $\endgroup$ Commented Jul 8, 2016 at 18:31
  • $\begingroup$ It references Jan's comment chemistry.stackexchange.com/questions/39540/… $\endgroup$
    – Mithoron
    Commented Jul 8, 2016 at 19:34

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