Note that the "axes on a phase diagram are generally not drawn to scale". ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations. Quote from: peacefulltortoise on January 21, , AM. The vapor pressure of iodine increases as temperature rises. Sublimation condition match when the vapor pressure of iodine gets higher than total enviromental gas pressure and. Iodine doesn't melt because sublimation occurs at temperature that is slightly above than room temperature.
Enthalpy Chemist Sr. The same kind of bonds let a compound condensate and solidify, so "only van der Waals" and similar reasons would tell why a compound both melts and evaporates easily, not why it sublimates, that is goes directly from solid to gas - why it evaporates about as easily as it melts.
My partial understanding is that in a solid, malecules attract an other through several points at once because they are properly organized, while in a liquid, only one or few points attracts them at a given instant. In this image of liquids and solids, molecules that are unsymmetric can touch an other with an unfavourable angle, attract an other a bit, and make a liquid, but are less probable to have the favourable orientation that lets them make a solid.
As well, deformable molecules can attract an other at one or few atoms, but have rarely the proper conformation to fit optimally an other and make a solid. So stiff and symmetric molecules solidify almost as easily as they condense, have a small liquid range and can under some pressures sublimate, while deformable and unsymmetric ones condense easily but need a much colder temperature to solidify, showing a wide liquid range.
In this system, we see iodine vapour only when the temperature is at In contrast, when we observe a sample of solid iodine in the bottom of an unsealed glass flask, at 20 o C and 1 atm pressure, the system is different from the idealized system just described. There is air in the flask, and we see a faint colour of iodine vapour. Although the vapour pressure of iodine is very low 0.
If the flask is unsealed, the iodine vapour can escape. Eventually, the iodine sublimes away, just like an ice cube in a freezer. In another application of the diagram, imagine starting slightly to the right of point 2, and raising the pressure, on a line rising vertically. Initially, the iodine is liquid, but will change to solid at some point. Skip to main Skip to footer.
October I am not perfect — and never will be. PDFs of both articles can be found with a Google search. Article a has a short video-clip worth watching. If you doubt this, let me put you in contact with my spouse. Phase diagram of iodine. A phase diagram describes the situation in which one is observing: a single chemical substance, in a closed system, under equilibrium conditions. I chose to use these data from Wikipedia : triple point: Liquid: 4. Of interest also is the vapour pressure of solid iodine Table 1.
To understand this, you need to understand a phase change to gas occurs when the total vapor pressure of substance in a condensed phase solid or liquid exceeds the atmospheric pressure. So, at a given temperature, if the atmospheric pressure is low enough, any substance will go from solid to gas i. To gain a better understanding of this process, I urge you to look at a phase diagram. This article from UWaterloo has a phase diagram for iodine, and explains some key points. For the other two halogens, you would need to find a table of their respective vapor pressures in their solid state, and the temperature range at which they exist in their liquid states.
Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Learn more. Sublimation of Iodine Ask Question. Asked 6 years, 1 month ago. Active 3 months ago. Viewed 21k times. Improve this question. Add a comment. Active Oldest Votes. Improve this answer. Ivan Neretin Ivan Neretin Iodine only sublimes at pressures lower than about 0.
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