I know metals like copper, silver and gold for example have vapor pressures at high temperature but do their vapor pressures still exist at standard temperatures (290 kelvin) and pressures (100 kilopascals)?

  • 4
    $\begingroup$ Of course they exist, it is just that they are low enough to be considered 0 for all practical purposes. $\endgroup$ – Ivan Neretin Jun 29 '17 at 13:42
  • 1
    $\begingroup$ Also, importantly, the vapor pressure is independent of external pressure. $\endgroup$ – Zhe Jun 29 '17 at 14:20
  • 2
    $\begingroup$ @Zhe What's it dependent on? $\endgroup$ – Mockingbird Jun 29 '17 at 14:33
  • $\begingroup$ Temperature only. $\endgroup$ – Zhe Jun 29 '17 at 15:09

This question has a couple of answers. But first we need to distinguish between a quantity or value existing and a quantity having a value of zero. I won't get into the weeds on that, but if you think about it, there is a clear difference between existence and non-existence on one hand and between zero and non-zero on the other. So, on to the question do these metals have a VP at STP? Yes. Is it greater than zero? Probably. Is it significantly greater than zero? Depends on what the purpose is for asking, that is:it depends on context. For most things, their STP VP is effectively zero because other sources of Cu, Ag, and/or Au contamination become dominant. Related factors to consider are: What is meant by a clean surface? Is VP really independent of P? (No) What is the lowest, most sensitive range over which we can measure (vapor) pressure? How good are our best man-made vacuums (Ultra-high vacuum)? In the real world, how well isolated are our most isolated physical systems (from leaks, neutrinos, cosmic rays, etc.)? To me, I consider a metal surface is almost never clean. It is quite difficult to clean - I mean really difficult. For a VP of zero, we require that an atom (of the metal) on the surface of the crystal face never ever obtains sufficient energy to break all of the bonds to its neighbors and has enough kinetic energy to escape the surface. I'd not expect that to happen very often at temperatures that are ~700 K less than the metals MP (and > 1700 K less than its BP). It is much more likely that migration across surfaces will dominate any signal detected, at least that type of problem would have to be ruled out. So, I'd sum up to say that while I'd expect almost all measurements to return a zero value, that I'd expect to see a stray atom of the metal from time to time, as well. The kinetic (statistical) theory of gasses is an infinite distribution of energies. That is, at temperatures above 0 K, the chances of an atom having near infinite energy is not zero (although it is near zero). Meaning the chances of an atom of the metal having enough energy to leave the metal surface is not zero. I'd suggest that that means theoretically the metals have a VP, while practically we may or may not be able to measure it. (I've not done a literature search, sorry.)


Not the answer you're looking for? Browse other questions tagged or ask your own question.