By definition, chemical properties are properties of a substance that can only be observed during a chemical change. Chemical changes are reactions that convert one or more substances into new substances. Therefore, chemical changes change the composition of the reactants.
Flammability is a chemical property because it can only be observed or measured during a chemical change known as combustion. Combustion is a chemical reaction that occurs when a fuel reacts with oxygen to produce light and heat.
Heat of combustion, pH, being corrosive, oxidation, and electronegativity are other examples of chemical properties.
On the other hand, physical properties of substances describe characteristics of physical states of substances. Density, melting point, boiling point, hardness, malleability, and solubility are examples of physical properties.