During an experiment, solid iodine was placed in a sealed container. The container was gradually heated and purple-colored vapors of iodine formed were observed. Describe this system when it reaches phase equilibrium.

The process is known as sublimation

Explanation:

Sublimation is a process wherby solid substances are changed into gaseous state

At equilibrium, solid iodine sublimes to give purple-coloured iodine vapour, which also condenses back to the solid iodine.

Explanation:

Sublimation is the process by which a solid changes state directly from the solid state to a gaseous state without going through the liquid state. Solid iodine is one of such solids that undergo sublimation.

  At equilibrium,            I₂ (solid)  ⇔  I₂(gaseous)

From the question,

As heat is gradually applied to the sealed container,  solid iodine begins to sublime and the purple-coloured vapour of iodine is observed.

As the heating continues, the intensity of the purple colour intensifies as more of the solid iodine undergoes sublimation.

At equilibrium however, it is observed that the intensity of the purple coloured iodine vapour remains the same.

This is so because at equilibrium, solid iodine sublimes to give purple-coloured iodine vapour, which also condenses back to the solid state

the answer is barium and copper bromide