Let us now consider the systems where solids sublime to vapour phase. If we place solid iodine in a closed vessel, after sometime the vessel gets filled up with violet vapour and the intensity of colour increases with time.
After certain time the intensity of colour becomes constant and at this stage equilibrium is attained. Hence solid iodine sublimes to give iodine vapour and the iodine vapour condenses to give solid iodine.
Other examples showing this kind of equilibrium are
NH4CL (solid) ⇔ NH4CL(vapour)
Camphor (solid) ⇔ Camphor (vapour)
