Why are freezing, condensation and deposition exothermic processes?
Because all of these slow molecular motion, i.e. require the extraction of heat from the system.
Exothermic by definition means the release of heat from a system. Any process that slows down the particles in the system due to heat flow outwards is therefore exothermic.
- Freezing has particles of a liquid slow down to form a lattice structure and become a solid phase.
- Condensation has particles of a gas slow down to form intermolecular forces and transition into a liquid phase.
- Deposition has particles of a gas slow down to form a lattice structure, becoming a solid and skipping the liquid phase.
Thus, the above three processes are exothermic with respect to the system.