Naphthalene balls sublime because they have a high vapor pressure at room temperature. This means that the molecules of naphthalene are able to escape from the solid phase and into the gas phase without first melting. The sublimation process is driven by the difference in the free energy of the solid and gas phases. At room temperature, the free energy of the gas phase is lower than that of the solid phase, so the molecules of naphthalene will tend to escape from the solid and into the gas phase.

The rate of sublimation increases with increasing temperature. This is because the higher the temperature, the greater the difference in the free energy of the solid and gas phases. The rate of sublimation also increases with increasing surface area. This is because the greater the surface area, the more molecules of naphthalene will be able to escape from the solid and into the gas phase.

Naphthalene balls are often used as a moth repellent because they release a gas that is toxic to moths. The gas is also toxic to humans, so it is important to use naphthalene balls in a well-ventilated area.