What conditions lead to the direct transition from gas to solid?

The direct transition from gas to solid, known as deposition, occurs under conditions of low temperature and high pressure.

Deposition is a phase transition that skips the liquid phase and goes directly from the gas phase to the solid phase. This process is the reverse of sublimation, where a solid turns directly into a gas. The conditions that lead to deposition are typically low temperatures and high pressures.

In the context of the kinetic theory of matter, the particles in a gas have a lot of kinetic energy and are moving around freely. When the temperature is lowered, the kinetic energy of the particles decreases. If the temperature is lowered enough, the particles will not have enough energy to overcome the attractive forces between them. As a result, they will come together and form a solid.

Pressure also plays a role in deposition. High pressure forces the particles closer together. When combined with low temperatures, this can cause the particles to arrange themselves into a solid structure.

An everyday example of deposition is the formation of frost. When the temperature drops on a cold night, water vapour in the air can change directly into ice without first becoming liquid water. This is because the low temperature and high pressure conditions are right for deposition to occur.

In summary, the direct transition from gas to solid, or deposition, happens when the temperature is low enough and the pressure is high enough for the gas particles to come together and form a solid. This is a fascinating aspect of the behaviour of matter that shows how changes in temperature and pressure can lead to dramatic changes in state.