If the temperature of a gas in a closed container increases: the pressure of the gas increases. the pressure of the gas decreases. the molecules collide with the walls of the container less frequently. the average kinetic energy of the molecules decreases.

Asubstance is held in an open container. its particles move past one another at random speeds but do not leave the container. heat is removed from the system, and the particles slow down. when enough heat is removed, the particles no longer have enough speed to overcome the weak attractive forces between them. when this happens, the substance enters its solid state. the process described above is known as .