Phase changes

[705801855]

Hi, how do we know whether phase changes are endothermic or exothermic?

[Rebecca Liu 2E]

Exothermic reactions will have a negative delta H value / overall net enthalpy, while endothermic has a positive delta H value. For phase changes, anything that involves breaking bonds (input energy required, so positive delta H value) is endothermic, such as vaporization, melting, and sublimation.

[Emily_Hanna_2E]

Hi! Vaporization (liquid to vapor), melting/fusion (solid to liquid), and sublimation (solid to vapor) are endothermic processes as heat is required for these processes to occur. Freezing(liquid to solid), condensation(vapor to liquid), and deposition(vapor to solid) are exothermic processes because heat is released during these processes. It helps to think of it as when heat is involved for the process to occur, it will be endothermic since heat is required/absorbed. Otherwise, it will be exothermic and heat will be released. Hope this helps!

[Jenny Tran 2B]

hey !

phase changes that involve going from a less disordered state to a more disordered state (such as vaporization) are endothermic. Phase changes from a more disordered state to a less disordered state (such as freezing and condensation) are always exothermic.

[Phanuphong Techasiri]

Phase changes can be determined as endothermic or exothermic based on the heat flow during the change. In an endothermic process, heat is absorbed and the temperature of the system decreases, while in an exothermic process, heat is released and the temperature of the system increases. The sign of delta H (enthalpy change) can also be used to determine if a process is endothermic or exothermic. If delta H is positive, the process is endothermic and if delta H is negative, the process is exothermic.

[Samuel Vansomphone 1H]

Changes from a more-ordered state to a less-ordered state are endothermic.
Examples include fusion, vaporization, and sublimation.

Changes from a less-ordered state to a more-ordered state are exothermic.
Examples include freezing, condensation, and deposition.

[Jarod Miller 2E]

Phase changes will be endothermic or exothermic based off whether they release or require heat. For example melting and vaporization requires heat meaning it’s an endothermic process while freezing and condensation would be considered an exothermic process because of releasing heat during the process.