A chemical change is a change in the chemical composition of a substance. This means that the atoms and molecules that make up the substance are rearranged or combined in a different way. A physical change, on the other hand, is a change in the physical properties of a substance without changing its chemical composition. This means that the atoms and molecules of the substance stay the same, but their arrangement or state may change.
For example, when water freezes, it undergoes a physical change because its molecules slow down and form a solid instead of a liquid. However, the chemical composition of water does not change, and it can be melted back into a liquid without changing its chemical structure.
On the other hand, when wood burns, it undergoes a chemical change because the cellulose and lignin molecules in the wood react with oxygen to form carbon dioxide, water, and ash. The chemical composition of the wood has been changed, and it cannot be burned again without undergoing another chemical change.
