The properties of the system which arise from the basic behavior of matter is known as microscopic properties of the system. Force, temperature, pressure, mass, volume, viscosity, surface area, surface tension etc. Microscopic properties of a system are of two types:
- Intensive property of the system: The property of the system whose value is independent of the amount of the substance present on the system is known as intensive properties of the system. For example: Temperature, pressure, viscosity, surface tension etc.
- Extensive property of the system: The property of the system whose value depends upon amount of substance present in the system is called extensive property of the system.
State of a system: The condition of a system which is described by its measurable properties is called the state of the system. When temperature, pressure, volume of a system is changed, the changes occur in the whole system. For example: the state of gaseous system can be described by specifying its pressure, temperature and volume as:
P1V1T1 (initial state) → P1V1T1 (Final system)
Ice (Initial state) → Liquid water (Final state)
State variable: The state of a system depends upon temperature, pressure, volume mass and composition. The rate of a system is changed by changing any of these properties. These properties are called state variable. A system is said to be in a thermodynamics state, when all of these variable are fixed.
State function: Any physical quantity is said to be a state function if the change in its value during the process depends only upon the initial and final state of the system. Some thermodynamics properties like internal energy (H), entropy (S) and free energy (G) only depends upon the state of the system and are independent of the path through which it is brought about. These properties are called state function. The absolute value of a state function cannot be determined. However the change in state function with the change in system can be determined.
Path dependent function: The properties of the system which depends upon the path followed by the system is called path dependent.