Condensation is the change of the physical state of matter from gas phase into liquid phase , and is the reverse of evaporation . It can also be defined as the change in the state of water vapor to liquid water when in contact with any surface. When the transition happens from the gaseous phase into the solid phase directly, the change is called deposition .
All the processes discussed on the preceding pages (vaporization, sublimation, and fusion) occur during a heat addition to a substance. If heat is removed from a substance, the opposite of the described processes will occur. As previously described, a heat addition at a constant pressure to a saturated liquid will cause the liquid to evaporate (change phase from liquid to vapor). If heat is removed at a constant pressure from a saturated vapor, condensation will occur and the vapor will change phase to liquid. So the processes of vaporization and condensation are the exact opposite of each other. Similarly, freezing is the opposite process of melting and fusion. Sublimation also has an opposite process in which a gas goes directly to solid, but this process is not normally referred to with a unique term.