* Chemical Properties: Describe how a substance reacts with other substances. They involve the formation of new substances with different compositions.

* Physical Properties: Can be observed without changing the substance's chemical composition. Examples include color, density, melting point, etc.

Reactivity describes a substance's tendency to undergo chemical reactions. For example, the reactivity of sodium metal is high, meaning it readily reacts with water, oxygen, and other substances. This reaction changes the chemical composition of sodium, forming new substances.

In contrast, a physical property like melting point describes a substance's transition from solid to liquid without changing its chemical makeup.