Intensive and extensive properties are the two classes of physical properties of matter. A physical property, in turn, is one which can be observed and measured without changing the chemical composition of the sample. Physical chemist and physicist Richard C. Tolman coined the terms “intensive” and “extensive” in 1917. Here is an explanation of what intensive and extensive properties are, examples of each type, and how to tell them apart.
Extensive and intensive properties are the two types of physical properties of matter.
Intensive properties do not depend on the amount of matter in a substance. Examples include state of matter, temperature, and density.
Extensive properties depend on the amount of matter in a sample. Examples include mass, length, and volume.
Intensive properties are also called bulk properties of intensive quantities. They do not depend on the amount of matter. These physical properties are used for sample identification because they are the same under different conditions and for all sample sizes. Examples of intensive properties include:
- Boiling point
- Electrical conductivity
- Magnetic permeability
- Melting point
- Surface tension
- State of matter
- Refractive index
Extensive properties are physical properties that do depend on the amount of matter in a sample. They are also known as extensive quantities. These properties are additive for subsystems. While extensive properties aren’t useful for sample identification, they are great for describing it. Examples of extensive properties include:
- Gibbs energy
- Heat capacity
The ratio between two extensive properties is a special type of intensive property called a specific property. As an example, both mass and volume are extensive properties. Their ratio is density, which is an intensive property and a specific property. Other specific properties include specific volume (the reciprocal of density), specific heat capacity (heat capacity divided by mass), molar volume (volume per mole), and specific enthalpy.
How to Tell Intensive and Extensive Properties Apart
The easiest way to tell whether a physical property is intensive or extensive is to take two samples of the same type of matter and combine them. An intensive property won’t change depending on sample size. A small amount of matter has the same density, temperature, and hardness as a large amount of the same substance. In contrast, an extensive property is additive. What this means is doubling the size of the sample doubles an extensive property. So, doubling the sample would make it twice as massive, twice as long, etc.
- IUPAC (1997). “Extensive quantity.” Compendium of Chemical Terminology (2nd ed.) (the “Gold Book”) Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford. doi:10.1351/goldbook.E02281
- IUPAC (1997). “Intensive quantity.” Compendium of Chemical Terminology (2nd ed.) (the “Gold Book”). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford. doi:10.1351/goldbook.I03074
- Redlich, O. (1970). “Intensive and Extensive Properties”. J. Chem. Educ. 47 (2): 154–156. doi:10.1021/ed047p154.2
- Tolman, Richard C. (1917). “The Measurable Quantities of Physics.” Phys. Rev. 9 (3): 237–253.