ACS Physical Chemistry: Thermochemistry Practice Test 2026 – The Complete All-in-One Resource for Exam Success!

Extensive properties are characteristics of a system that depend on the amount of material or size of the system. When the volume or quantity of a substance increases, the values of extensive properties, such as mass, volume, and energy, also increase proportionally. This means that if you double the amount of substance in a system, the extensive properties will also double.

Because extensive properties vary with size, they provide insights into how the system's characteristics change as the amount of substance changes. This distinction is critical in thermodynamics as it helps in understanding how systems respond to changes in size or quantity.

In contrast, intensive properties, such as temperature and pressure, remain constant regardless of the amount of substance present in a system. This clearly delineates extensive properties as those that are directly influenced by the size or quantity of the substance involved.