Explanation of sublimation of water.

Sublimation can be defined as the transition of water molecules from the solid state (ice) directly into the gaseous state (vapor) without going through the liquid state. The sublimation point can be defined as the temperature at which vapor and ice coexist in equilibrium. According to the Phase Rule, the number of components, C, is equal to 1, the number of phases at equilibrium, P, is equal to 2, and the number of degrees of freedom is equal to 1. This means that we need to mention at least one variable to fully describe water at the sublimation point. This variable can either be temperature or pressure. Sublimation of pure water can only occur at low pressure values that are below the triple point.