Sublimation and deposition

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Sublimation

Figure 1: A piece of solid carbon dioxide (dry ice) sublimating from a solid directly into a gas.[1]

Sublimation is a type of phase change that takes place when a solid turns directly into a gas, skipping the liquid phase. The opposite of sublimation is vapour deposition. The term "sublimation" only applies to a physical change of state and not to the transformation of a solid into a gas during a chemical reaction.[2]

One common example of sublimation is solid carbon dioxide, known as dry ice. At room temperature (293 K) and pressure (1.01 Bar), dry ice sublimates into carbon dioxide vapor. Sublimation is an endothermic process that happens below a substance's triple point in its phase diagram.[3] Figure 2 shows a phase diagram for carbon dioxide where sublimation would occur below the triple point (216.55 K and 5.17 Bar).[4] This means that liquid carbon dioxide is possible, it just requires 5 times normal atmospheric pressure in order to get the liquid to form. The temperatures and pressures under which sublimation happens depends on the chemical and physical properties of the system. The energy associated with a transition from solid directly to gas is called the latent heat of sublimation.

Sublimation also happens with snow. This means that when the air is particular dry (low humidity) the water turns directly from snow or ice into water vapour without being liquid at all.[2]

Figure 2: Phase diagram of carbon dioxide showing how sublimation happens below the triple point.[5] Higher pressures would make the dry ice look 'wet', since liquid carbon dioxide would form.

Visit UC Davis' Chem wiki for more information on sublimation.

Deposition

As stated earlier, vapour deposition is the opposite of sublimation. Deposition is when a substance in gas form changes states to become a solid. The gaseous substance gets deposited (usually as crystals) bypassing the intermediate liquid state. An example of deposition is when water vapor in the atmosphere changes directly into ice, such as the formation of frost.[2]

For Further Reading

References

  1. Helmenstine, Anne Marie, Ph.D. "Sublimation Definition (Phase Transition in Chemistry)," ThoughtCo, Feb. 16, 2021. [Online]. Available: thoughtco.com/definition-of-sublimation-phase-transition-604665. [Accessed: 12-May-2021]
  2. 2.0 2.1 2.2 "Sublimation and the water cycle", USGS [Online]. Available: https://www.usgs.gov/special-topic/water-science-school/science/sublimation-and-water-cycle?qt-science_center_objects=0#qt-science_center_objects [Accessed: May 13th, 2021.]
  3. "Sublimation (physics)," World Heritage Encyclopedia. [Online]. Available: http://self.gutenberg.org/articles/Sublimation_(physics). [Accessed: 14-May-2021]
  4. "Phases of matter," UCSB Physics. [Online]. Available: http://web.physics.ucsb.edu/~lecturedemonstrations/Composer/Pages/48.36.html. [Accessed: 12-May-2021]
  5. "Supercritical carbon dioxide," Wikipedia, 2021. [Online]. Available: https://en.wikipedia.org/wiki/Supercritical_carbon_dioxide. [Accessed: 12-May-2021]

Authors and Editors

Dayna Wiebe, Jason Donev
Last updated: October 15, 2021
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