Final answer:
Phase changes are physical processes in which materials change states; they can be endothermic, which absorb energy (sublimation, vaporization, melting/fusion) or exothermic, which release energy (deposition, condensation, freezing).
Step-by-step explanation:
Phase Change Processes
Listed below are the phase change processes and whether they are endothermic or exothermic:
- Sublimation (solid to gas) - Endothermic: energy is absorbed during the direct conversion of a solid to a gas.
- Vaporization (liquid to gas) - Endothermic: energy is absorbed when a liquid changes into a gas (includes boiling and evaporation).
- Melting/Fusion (solid to liquid) - Endothermic: energy is absorbed to convert a solid to a liquid; also known as the enthalpy of fusion (ΔHfus).
- Deposition (gas to solid) - Exothermic: energy is released during the direct conversion of a gas to a solid.
- Condensation (gas to liquid) - Exothermic: energy is released when a gas changes into a liquid.
- Freezing (liquid to solid) - Exothermic: energy is released when a liquid becomes a solid; also known as the enthalpy of fusion reverse process.
All phase changes occur under the principle that the transition to a more ordered state is exothermic, while the movement to a less ordered state is endothermic. During phase changes, if the substance goes to a less energetic state such as during freezing or condensation, it generally releases heat. Conversely, if it goes to a more energetic state such as during vaporization, melting, or sublimation, it absorbs heat from the surroundings.