When a substance goes directly from a solid state to a gas, this process is called sublimation.

Dry ice (solid carbon dioxide) is a great example of a substance that undergoes sublimation. This occurs because the vapor pressure of dry ice at atmospheric pressure is higher than the pressure of the surrounding environment. As a result, the CO2 molecules on the surface of the dry ice have enough energy to break free from the solid state and transition directly into the gas phase.