Why Is Density an Intensive Property?

Intensive properties are defined as properties of matter than do not change as the amount of matter changes. In science, density is defined as mass per unit volume. Each chemical compound has a certain constant density regardless of amount present, making density an intensive property. Whether 2 kilograms or 2 grams of a substance is present, if the mass is divided by volume present, the result is the same value.

Properties of matter are divided into two categories: intensive and extensive. While intensive properties, such as density, boiling point and freezing point, do not change as the amount of matter present changes, extensive properties do change as the amount of matter present changes. Both mass and volume are extensive properties. However, density is a ratio of these two properties, and the ratio does not change, making density an intensive property.

As a general rule in thermodynamics, the ratio of any two extensive properties is always an intensive property. Two other related extensive properties are mass and the number of moles of a given substance present. While both of these values are dependent on the amount of the substance present, the ratio of mass to number of moles present is an intensive property known as molar mass. Water, for example, has a molar mass of 18 grams per mol. This is true whether 20 grams or 200 grams of water are present.