Deposition
Definition and meaning of Deposition in chemistry.
Deposition is the phase transition in which a substance changes directly from a gas (vapor) into a solid, without passing through the liquid state.
In more detail
Deposition occurs when vapor is cooled or its pressure is otherwise brought below conditions that would allow a stable liquid, so molecules pack directly into an ordered solid lattice. Because the gas loses much more kinetic and potential energy in becoming a solid than it would in merely condensing to a liquid, deposition is a strongly exothermic process, releasing both the latent heat of condensation and the latent heat of fusion. It is the reverse of sublimation, and both processes occur on either side of a substance's triple point on its phase diagram. Deposition is important in meteorology (frost and snow formation), industrial processes like physical vapor deposition for thin films, and purification techniques.
Key facts
| Field | Physical Chemistry |
|---|---|
| Reverse process | Sublimation (solid to gas) |
| Energy change | Exothermic (releases heat) |
| Common example | Frost formation from water vapor (H2O) |
On a cold, clear night, water vapor in humid air contacts a car windshield below 0°C and deposits directly as a thin layer of ice crystals (frost), bypassing the liquid dew stage entirely.
Frequently asked questions
Is deposition the same as condensation?
No. Condensation converts a gas into a liquid, while deposition converts a gas directly into a solid, skipping the liquid phase entirely.
Where does deposition occur on a phase diagram?
It occurs along the solid-vapor equilibrium curve, at temperatures and pressures below the substance's triple point, where the liquid phase is not stable.