A physical change is a modification that is induced in a substance which does not change the substance’s chemical makeup. Thus, the term physical change is in direct contrast with the term chemical change. We see the effects of physical changes every day, whether we realize it or not.
The first example of a physical change is a rather obvious one, but yet it is often overlooked. When a substance undergoes a phase or state change (such as melting, freezing, etc.), it has undergone a physical change. This becomes important if we write out an enthalpy equation for a state change. For example, if enough energy is added to a certain volume of liquid water that it would evaporate, that water is still composed of hydrogen and oxygen atoms, they are simply in a different state.
Another set of common physical changes are the properties of malleability and ductility. Put simply, malleability is the property to be hammered out into a sheet, and ductility is the property to be drawn out into a wire. For example, when Steel is hammered into sheets for use in an automobile or copper is stretched into a wire for electronic use, they have undergone a physical change.
Again an obvious change, but the mixing of two solids into a homogeneous or heterogeneous mixture is also a physical change. If one was to mix salt and sugar, the mixture would have properties of salt and sugar proportionally to the quantities of solids used to create the mixture. This is because the only part of the solids that have changer were their location in space, and being in the presence of another solid means that a chemical change cannot have taken place.
The last type of physical change is extremely common, and it is the division of a solid. An action as simple as the breaking of glass is considered to be a physical change, because although there are now different amounts of glass in different spatial locations, the glass is still glass, it is not a fundamentally different material. For this reason, we classify an action such as the breaking of solid glass to be a physical change.
Physical changes are extremely important in the known universe, but their simplicity is often overlooked. By using a rational thought process about the chemical structure of the substance involved, we can use process of elimination to check whether or not a physical change has actually taken place.
