Solid-Vapour
 equilibrium 
simulation

Two subdivision states of the solid are considered. Motion and exchanges between the two phases are introduced by clicking "play" and are maintained for about 1 minute, it being possible to stop the motion and step through the simulation one frame at a time. 

For simplification, the molecules are represented by circles, and thus the only motion in the gas phase shown is translational; for the solid aggregates, vibrations are shown as though iodine was monoatomic. The (microscopic) rates of the opposite changes s"g and g"s are represented by the vertical arrows on the sides. The (equal) lengths of the pointing up s"g arrow and of the pointing down g"s arrow are proportional to the (equal) rates. Vertical bars are also shown to give the number of exchanges between the two phases since the beginning of the simulation. We note that only equilibrium states are represented and not any evolution towards equilibrium.