STATES OF MATTER - properties of gases and liquids (fluids) and solids
12. The special case of sublimation (solid <=> gas)
Doc Brown's chemistry revision notes: basic school chemistry science GCSE chemistry, IGCSE chemistry, O level and ~US grades 8, 9 and 10 school science courses or equivalent for ~14-16 year old science students for national examinations in chemistry and also helpful for UK advanced level chemistry students aged ~16-18 and US grades 11-12 K12 honors.
Examples of sublimation explained using the kinetic particle theory of gases and solids
The opposite of sublimation is sometimes referred to as deposition or 'reverse sublimation'.
Theory in terms of particles:
Examples of sublimation:
The formation of a particular
frost involves the direct freezing of water vapour (gas).
Frost can also evaporate directly back to water vapour (gas) and this
happens in the 'dry' and extremely cold winters of the Gobi Desert on a
H2O (g) (physical change only) See pictures of 'hoar frost'
and the process of freeze drying food in sections below.
H2O (s) H2O (g) (physical change only)
See pictures of 'hoar frost' and the process of freeze drying food in sections below.
The liquid particle picture
does not figure here, but the other models fully apply apart from state
changes involving liquid formation.
particle model and
particle model links.
You can also use the reverse reaction to illustrate diffusion and the fact
that the rate of diffusion depends on the molecular mass See section 4.
of demonstrating diffusion in gases
You can also use the reverse reaction to illustrate diffusion and the fact that the rate of diffusion depends on the molecular mass See section 4. Examples of demonstrating diffusion in gases
PLEASE NOTE,At a higher level of study, you need to study the g–l–s phase diagram for water and the vapour pressure curve of ice at particular temperatures. For example, if the ambient vapour pressure is less than the equilibrium vapour pressure at the temperature of the ice, sublimation can readily take place. The snow and ice in the colder regions of the Gobi Desert do not melt in the Sun, they just slowly 'sublimely' disappear!
The formation of hoar frost - the reverse of sublimation
Frost is a thin layer of ice on a solid surface.
Hoar frost forms directly from water vapour in air above 0oC, coming in contact with a solid surface whose temperature is below freezing (<0oC).
The water vapor changes directly from gas (vapour) to solid (ice) as it comes into contact with the solid surface.
How freeze drying food works
Learning objectives for sublimation reverse sublimation (deposition)
Know what we mean by sublimation, the interchange of vapour/gas and solid without an intermediate liquid state of matter.
Be able to draw particle pictures to illustrate and explain sublimation and its reverse i.e. deposition..
Be able to use the kinetic particle theory of matter to explain the state of matter change of sublimation,
Know that thermal energy must be absorbed by a solid before it can be sublimed.
Know that iodine and ammonium chloride are good examples of solids to heat and observe the phenomenon of sublimation.
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