In physics and chemistry, extensive properties depend on the amount of substance in a system, while intensive properties do not. Examples include mass and volume, while density is an example of an intensive property. Internal energy, entropy, Gibbs free energy, and enthalpy are extensive properties in thermodynamics. Specific properties are intensive. Confusion can arise between extensive properties and system perceptions.
In physics and chemistry, an extended property of a substance is a property that depends on the amount of that substance in a physical system. Conversely, intensive properties do not depend on the amount of material in the system: the intensive properties of a substance will not change no matter how much there is. Popular examples of a substance’s broad properties include its mass and volume.
One of the most basic illustrations of the differences between extensive and intensive properties can be found in the density property. The density of an object can be found by dividing the mass of an object by its volume. Its mass and volume are said to be extended properties because they depend on the amount of material in the object: the more material, the greater the mass and volume. Assuming the composition of the object is uniform, however, the density will remain the same regardless of size.
An easy way to remember the differences between an intensive property and an extensive property is that when two identical systems are combined, the intensive properties will remain the same while an extensive property would be doubled. For example, connecting two identical gas cylinders with identical contents would double the mass of the system, which is an extended property. The pressure inside the containers is intense and would remain the same.
In thermodynamics, internal energy, entropy, Gibbs free energy, and enthalpy are said to be extended properties. Their quantities depend on the dimensions of the thermodynamic system. These values should not be confused with specific energy, specific entropy, specific Gibbs free energy or specific enthalpy, which are intensive.
In general, an extensive property divided by another extensive property will result in an intensive property. Density, expressed as the ratio of mass to volume, is one example. The specific properties of thermodynamics are also intense. For example, the specific heat capacity of a substance can be expressed as the ratio of the heat capacity of the substance to the mass of the substance.
There is most commonly confusion regarding the differences between extensive properties and intensive properties, but there is also confusion between extensive properties and system perceptions. A perception about a particular system describes an observer’s thoughts about an abstract concept, such as color or smell. Unlike an abstract concept, an extended property can be quantified and measured.
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