Talk:Sublimation (chemistry)

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(William M. Connolley 09:58, 2004 Apr 17 (UTC)) Being picky... why is this page sublimation (chemistry) not sub (physics)? On the grounds that chemistry is for reactions and stuff.

Good point. I support that change. Mike Simpson 05:51, 24 Jun 2004 (UTC)

Third time's a charm... done! –radiojon 02:24, 2004 Jun 30 (UTC)

[edit] sublimation

another definition sublimation is a type of evaporation in which a solid changes directly to a gas without going through a liquid state.

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Can this word be correctly used to discribe the loss of moisture content in snow in extremly cold subfreezing tempertures ?

Yes, that is exactly what happens.

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Webster's 8th Collegiate (1977) uses, in our physics (or physical chemistry) realm:

• the verb sublime in two explicitly distinct ways:
  1. (intransitive verb, of a solid) To pass directly to vapor, without implication as to its further fate.
  2. (transitive verb) To cause a solid to pass directly to vapor, and then back to solid. (Note that this is analogous to distillation, and can purify the material (transform it into something "sublime") by either leaving behind a substantially less volatile impurity that doesn't vaporize with it, or converting a volatile impurity back to solid at a different location (with a higher or lower temperature) than where the desired material solidifies).
• the verb sublimate only as a synonym for the transitive ("round-trip") version.
• the noun sublimation only as being derived from the transitive ("round-trip") version.

That is to say, for them, "to sublimate" may involve conversion from vapor to solid, but they imply it is applicable to conversion from vapor to solid only when direct conversion from solid to vapor has preceded it as part of an overall process.

In contrast,

• Our first 'graph says in its first sentence (emphasis supplied)

  conversion between the solid and the gaseous phases ...

and its second sentence (the triple-point discussion) says "phase transition", in both cases without restricting the direction of the "conversion" or "transition", all but saying that vapor to solid without liquid, and no matter how the vapor is obtained, is an instance.

• Our final 'graph says

  The opposite of sublimation is deposition. The formation of frost is an example of deposition

all but saying that "deposition" is never an instance of sublimation.

• The text of the article in between gives fairly specific examples of solid to vapor, with the only reference to deposition being that of deposition after S->V conversion, in the case of printing by dye sublimation.

IMO, our article is probably using "sublimate" with either

• one definition that admits to 3 cases (S->V, V->S, & round-trip), and is inconsistent with either of the Web Coll defintions, each of which admits to only one of those three cases, and excludes the one-way V->S case, or
• different editors have focused on two or three different definitions, without ever acknowledging that more than one exists, much less that more than one is in use in the article.

And while we're at it, we use

• sublimation three times (plus title),
• sublimate four, and
• sublime once,

without explicitly specifying their relationships.

I'll look at some bigger dictionaries, but i'd love to have someone pre-empt my impending editing spree.
--Jerzy(t) 09:26, 2005 Feb 8 (UTC)

Good news: Amer. Her. Dict. supports all of our usages; IMO we've got the facts straight, and all that's needed is

• to make the distinctions
  • among the 3 cases, and
  • between transitive and intr.,
• to be consist in using "sublimate" rather than "sublime",
• and to mention that "sublime" is neither preferred nor incorrect.

--Jerzy(t) 16:38, 2005 Feb 8 (UTC)

[edit] Sublimation of ice

I've reverted the edit by User:Jgassens, which said that ice at temperatures below the freezing point of water does not sublime except at low pressures. This is a common misconception, but anyone who has seen their ice cubes shrink in their freezer has seen the sublimation in action. What matters is the partial pressure of water (also see vapor pressure): if it is below the pressure for the solid-vapor equilibrium as seen in the the phase diagram, the solid will sublime until that pressure is reached (which for an open system in a dry environment won't happen, so all of the ice will sublime). If it is above the equilibrium pressure, the vapor will deposit on the solid until the pressure reaches the equilibrium. If the partial pressure of water is at its equilibrium value, nothing will seem to happen, but microscopically there is still sublimation and deposition going on with equal rates, resulting in a dynamic equilibrium.

This is the exact same situation as for iodine. Dry ice is different becase, at 1 atm, it is below the pressure of the triple point, which means that not only one sees sublimation, but also there is no way of having liquid CO2 at any temperature (at 1 atm). Itub 16:16, 6 February 2006 (UTC)

[edit] Deposition of water

The article states that formation of frost is an example of deposition, yet the phase diagram for water shows that this is not possible. The water vapor must first turn into a liquid before it can turn into a solid, because the pressure is not low enough for deposition to occur.

Here is a phase diagram for reference: http://encarta.msn.com/media_461541579/Phase_Diagram_for_Water.html