Examples of Extensive and Intensive Properties in Chemistry and Physics

Understanding the distinction between extensive and intensive properties is critical for comprehending the behavior of matter in various scientific contexts. These properties play a vital role in fields like chemistry and physics, providing essential information that aids in the characterization of materials and the prediction of their behavior under different conditions.

What are Extensive and Intensive Properties?

Extensive and intensive properties are two primary categories of physical properties used to describe matter. Extensive properties depend on the quantity of substance present, while intensive properties remain constant regardless of the amount of material.

Extensive Properties

Extensive properties are those that depend on the amount of substance. They change when the size or amount of the material changes. Here are some examples:

Mass: The quantity of matter in a substance. This is a clear example of an extensive property because doubling the amount of a substance would also double its mass. Volume: The amount of space a substance occupies. Like mass, volume is extensive as it scales with the amount of substance. Length: The measurement of an object from one end to the other. Length is also an extensive property as it increases with the size of the object. Total Energy: The sum of all forms of energy in a system. Any addition or subtraction to the system leads to a change in the total energy, making it an extensive property. Entropy: A measure of the disorder or randomness in a system, which can vary with the amount of substance. Entropy is extensive, as it increases with the number of particles in the system.

Intensive Properties

Intensive properties, in contrast, do not depend on the amount of substance present. These properties remain constant regardless of the amount of material. Here are some examples:

Density: The mass per unit volume of a substance, such as grams per cubic centimeter. Density is an intensive property because it does not change when the amount of the substance is altered. Temperature: A measure of the average kinetic energy of the particles in a substance. Temperature remains constant irrespective of the amount of material. Pressure: The force exerted per unit area. Pressure is another example of an intensive property as it does not vary with the size of the system. Color: The characteristic of light as perceived by the human eye. Color is also an intensive property as it does not depend on the amount of the substance. Melting Point: The temperature at which a substance changes from solid to liquid. This property is independent of the sample size, making it an intensive property.

Clarifying the Definition of Extensive and Intensive Properties

It's important to clarify that extensive and intensive properties are not concepts, but rather definitions made for convenience. Extensive properties depend on the size of the system, whereas intensive properties do not depend on the size.

For example:

Temperature and Pressure are intensive properties. The temperature and pressure in a room remain the same even if the room is divided into smaller partitions. However, the volume of each partition changes. Volume, on the other hand, is an extensive property. As the volume of the system increases, so does its volume.

A key relationship exists between extensive and intensive properties. For each extensive property, one can find a corresponding intensive property by dividing the extensive property by the mass or number of moles of the system. For example, the specific volume (v) is calculated by dividing the volume (V) by the mass (m) of the system:

v V / m

It's important to note that this relationship is not always reversible. The specific volume (v) is simply the reciprocal of the density (ρ), so v 1 / ρ.

Why Define and Use Intensive Properties?

Tabulating relationships between properties for extensive properties would be impossible due to the wide range of possible quantities of matter. However, it is quite straightforward to tabulate relationships between intensive properties, such as per unit mass. By using these intensive property relationships, one can always revert to the extensive property by multiplying by the mass of the system.

Thus, the distinction between extensive and intensive properties is made for convenience, allowing for more manageable and practical calculations in chemistry and physics.