A chemical change is a change in the composition of atoms that make up a compound, or element, A physical change is a change in the state of the compound or element with no change in composition.
A chemical change like the formation of water has a change in the composition of the atoms.
The diatomic molecules of the elements Oxygen and Hydrogen have been changed into a triatomic Compound of Water
This is a chemical change.
A physical change like the evaporation of water has a change in the physical state of the compound
This is a physical change because the chemical composition of the water has not changed. but it has changed state from a liquid to a solid.
A chemical change is the formation of salt sodium chloride
This is a chemical change because the two dangerous elements have become a beneficial compound salt.
A physical change is the formation of salt water.