When we keep the temperature constant,
but increase the pressure on a quantity of gaseous substance
(e.g. water vapor), then we may observe the transition
from gas to solid at a certain pressure.
This process is called
deposition
or desublimation.
An example of deposition is when water vapor changes
directly to ice without first becoming a liquid,
causing frost (geada) on fields and cars.
In the figure below we start at the gas phase indicate by
1
to end up at the liquid phase indicated by 2.
Gas to solid at constant temperature
The opposite proces,
sublimation,
from 2
to 1,
happens when we decrease the pressure
on a solid under constant temperature.
