Explain the equilibrium when sublimation of solid takes place in a closed vessel.

(N/A) At a constant temperature in a closed vessel,the system where solids sublime to the vapour phase is known as solid-vapour equilibrium.
$Ex.-1$: If we place solid iodine $(I_2)$ in a closed vessel,after some time the vessel gets filled up with violet vapour and the intensity of the colour increases with time.
After a certain time,the intensity of the 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.
Properties,colours,etc.,become constant.
The equilibrium can be represented as: $I_{2(s)} \rightleftharpoons I_{2(g)}$ (constant $T$).
Other examples showing this kind of equilibrium are:
$(i)$ $Camphor_{(s)} \rightleftharpoons Camphor_{(g)}$ (constant $T$)
$(ii)$ $NH_4Cl_{(s)} \rightleftharpoons NH_4Cl_{(g)}$ (constant $T$)