What is the difference between a physical and a chemical property?

Without requiring a substance to undergo any chemical changes—that is, without breaking any bonds or changing its chemical composition—physical properties can be measured and observed.

Physical attributes therefore include things like color, melting and boiling points, density, hardness, and so forth.

Chemical properties, such as heat of combustion, can only be measured by burning the substance; enthalpy of formation, on the other hand, can only be measured by forming a (new) substance. Chemical properties can only be observed and measured by causing changes to the substance on an atomic/molecular scale through the formation or breaking of chemical bonds.

Chemical properties, on the other hand, describe how a substance behaves in reactions with other substances that result in changes to its chemical composition. Physical properties are the characteristics of a substance that can be observed or measured without changing the substance's chemical composition.