Matter can be described by its composition or by the way it looks, feels, or reacts in different situations. Each of these descriptions is a physical property or a chemical property of matter.
A physical property is a measurable state or attribute that can be observed without changing the composition of a substance. For example, color, taste, smell, volume, and mass are physical properties. A physical property of copper(II) sulfate in the crystalline state and in an aqueous solution is its blue color. Its chemical composition, CuSO4, however, is not a physical property.
Physical properties can be further categorized as intensive physical properties and extensive physical properties. An intensive physical property is a characteristic of a substance that is independent of the amount of the substance. Even if the quantity of the substance changes, the intensive physical property remains the same. For example, the hardness of a substance such as diamond is not determined by the size of the diamond. Regardless of the size of the diamond, its hardness is the same. Other examples of intensive physical properties include density, temperature, color, and luster.
An extensive physical property is a characteristic of a substance that depends on the amount of the substance. If the quantity changes, the extensive physical property changes. For example, mass is an extensive physical property. If the amount of substance increases, then its mass increases, and if the amount of substance decreases, then its mass decreases. Other extensive physical properties include volume, length, and weight.
A chemical property is a characteristic of matter that can be observed through a change in the composition of a substance. It describes the effects of a substance reacting with other substances. When a chemical change occurs, chemical bonds in the substances break and form, producing a new substance. This change is often irreversible. Some examples of chemical properties include how substances combust, react with acids, and rust.
Physical and Chemical Properties
| Substance | Physical Property | Chemical Property |
|---|---|---|
| Wood | Rough texture | Flammable |
| Iron | Shiny and ductile (can be pulled into wires) | Reacts with moist air, or rusts, to form a brown solid |
| Baking soda (NaHCO3) | White powder | Neutralizes weak acids |
| Copper(II) sulfate (CuSO4) | Blue crystals | Decomposes at 200°C |
| Molecular hydrogen (H2) | Colorless gas | Reacts with oxygen under certain conditions to form water |
Observing a chemical property requires a change in substance, but observing a physical property does not.