the process of direct change from solid to vapour is known as
Deposition (phase transition) Deposition is a thermodynamic process, a phase transition in which gas transforms into solid without passing through the liquid phase. The reverse of deposition is sublimation and hence sometimes deposition is called desublimation.
Chemical substance Chemical substances exist as solids, liquids, gases, or plasma, and may change between these phases of matter with changes in temperature or pressure. Chemical substances may be combined or converted to others by means of chemical reactions.