Sublimation: the transition of a substance directly from the solid to the gas phase without passing through an intermediate liquid phase; an endothermic phase transition that occurs at temps and pressures below a substance's triple point in its phase diagram; reverse is desublimation or deposition; as you observe an ice crystal in freezing air, an occasional molecule will gain enough energy to break away from its neighbors and enter into the air above
Energy Changing Processes: In this video Paul Andersen explains how energy can enter and leave a system. The amount of energy a substance can receive through heating or lose through cooling is measured using the specific heat capacity. Phase changing energy from solid to liquid is known as the enthalpy of fusion and phase-changing energy from a liquid to a gas is known as the enthalpy of vaporization. The energy leaving or entering a chemical reaction is the enthalpy of reaction.
Calorimetry: n this video Paul Andersen describes the history of calorimetry and explains how it can be used to measure energy changes in a system. The specific heat of water is well established and so as a system releases or absorbs energy from a surrounding water bath it can be measured. Calorimeters can be used to measure the specific heat capacity of a substance as well as the enthalpy of fusion, vaporization, and reaction.