Every substance has certain characteristics that distinguish it from other substances and that may be used to establish that two specimens are the same substance or different substances. Those characteristics that serve to distinguish and identify a specimen of matter are called the properties of the substance. For example, water may be distinguished easily from iron or gold, and-although this may appear to be more difficult-iron may readily be distinguished from gold by means of the different properties of the metals.
The properties related to the state (gas, liquid, or solid) or appearance of a sample are called physical properties. Some commonly known physical properties are density, state at room temperature, color, hardness, melting point, and boiling point. The physical properties of a sample can usually be determined without changing its composition. Many physical properties can be measured and described in numerical terms, and comparison of such properties is often the best way to distinguish one substance from another.
A chemical reaction is achange in which at least one substance changes its composition and its set of properties. The characteristic ways in which a substance undergoes chemical reaction or fails to undergo chemical reaction are called its chemical properties. Examples of chemical properties are flammability, rust resistance, reactivity, and biodegradability