All matter is made up of atoms. Atoms establish bonds with other atoms to form molecules. These bonds are firmly established and are unchanged. It is this chemical composition that distinguishes one compound from another. Yet, two compound with the same chemical makeup may look dramatically different. For example, water, ice, and vapor all contain the same water molecule, which consists of two hydrogen atoms bound to one oxygen atom (H2O), but each exists in a different state of matter. The transition between the solid, liquid, or gas state is one type of physical change a compound undergoes. So what is a physical change?
Physical Change
A physical change is any alteration in the physical characteristics of a compound that doesn’t affect the underlying chemical composition. This usually includes the size, shape, and color of a substance. For example, an intact glass jar and pieces of glass from a broken glass jar consist of the same chemical composition. The breaking of the glass jar into many glass pieces is a physical change.
States of Matter
Melting ice changes the state of matter of the water molecules from the solid state to a liquid state. The individual water molecules retain their chemical composition, but the interactions between two or more water molecules is affected. They are not as close together as they were in the solid state. If the liquid is further heated, the molecules will be further apart, resulting in vapor.
Physical Properties
The above example establishes one of the physical properties of matter: density. Density is a ratio of mass to volume. When the state of matter changes, its density changes as well. The temperature at which a compound changes its state of matter, such as the melting point and boiling point, are physical properties as well.
Reference:
Physical and Chemical Properties – ChemTeam
What is a Physical Change? – EdInformatics