sublimation
The direct conversion of a solid to a gas, without an intervening liquid phase, is calledsublimation. The amount of energy required to sublime 1 mol of a pure solid is theenthalpy of sublimation Hsub . Common substances that sublime at standard temperature and pressure STP; 0C, 1 atm include CO2 dry ice ; iodine Figure 11.18 "The Sublimation of Solid Iodine" ; naphthalene, a substance used to protect woolen clothing against moths; and 1,4-dichlorobenzene. As shown in Figure 11.17 "The Three Phases of Matter and the Processes That Interconvert Them When the Temperature Is Changed", the enthalpy of sublimation of a substance is the sum of its enthalpies of fusion and vaporization provided all values are at the same T; this is an application of Hesss law. For more information about Hesss law, see Chapter 5 "Energy Changes in Chemical Reactions", Section 5.2 "Enthalpy" . Equation 11.3.