On our planet, matter is essentially present in three different forms or states of aggregation: the solid state, the liquid state and the gaseous state. Each of them presents observable properties that are characteristic of it. Thus, solids have their own shape and volume; liquids, on the other hand, although they adopt the shape of the container that holds them, have a volume of their own that remains constant even when subjected to considerable external pressures. Gases, however, take the form of the container that contains them and occupy its entire volume.
The three general states of matter are dynamic, i.e., a body can present itself in the three physical forms (arrangement) by varying, for example, their temperature. This defines a physical change. When this occurs, the transformation does not affect the composition of the substance, but only involves a rearrangement of its atoms. It is important to mention that all physical transformations are reversible, i.e., the substance can return to its initial state of aggregation.
In summary, a physical change is a variation in the states of matter that a compound can undergo. In this type of event, the intimacy of the compound is not affected. On the other hand, in this type of change, it can go in one direction or the other. That is, if it has both directions it is reversible and if it has only one it is irreversible.
All changes of state are accompanied by energy expenditure or gain. Melting, evaporation (vaporization) and sublimation occur with energy absorption, while solidification, freezing (in the case of water), condensation (liquefaction) and inverse sublimation occur with energy release.
Those changes in the state of aggregation that are accompanied by temperature variation and absorption of heat energy are called endothermic, while the opposite processes are known as exothermic.
