考試要....急....Physical Change----sublimation...

Sublimation of an element or substance is a conversion between the solid and the gas phases with no intermediate liquid stage. Sublimation is a phase transition that occurs at temperatures and pressures below the triple point (see phase diagram).

At normal pressures, most chemical compounds and elements possess three different states at different temperatures. In these cases the transition from the solid to the gaseous state requires an intermediate liquid state. However, for some elements or substances at some pressures the material may transition directly from solid to the gaseous state. Note that the pressure referred to here is the vapor pressure of the substance, not the total pressure of the entire system.

The opposite of sublimation is deposition. The formation of frost is an example of meteorological deposition.