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Property and State

1.6.1 Property

The characteristics of a substance which are measurable or calculated is called property of the system. For example; pressure, volume and temperature which are macroscopic in nature. The properties which are independent of mass, such as pressure, temperature, specific volume are called intensive properties.

The properties which are dependent of mass such as volume, energy are called extensive properties.

 

Fig. 1.4. (n) shows a mass of substance (111}, volume V; and temperature T. A diaphragm is put in the mid way of the container. The two chambers (Fig. 1.4 (b)) thus formed have volume V / 2 mass m / 2  but P, T and specific volume v 1s the same. So V denotes extensive property a11d P, T and v denote intensive properties of the substance.

 

1.6.2 State

A state is the condition of a system which has definite properties and when can be represented at a point in the thermodynamic property coordinates such as (P, v) coordinate.

fig. 1.5 shows point 1 wbich is at s tate (P1 v 1) and 2 at (P2 v2) . When the system undergoes a change from state 1 to state 2, heat or work transfer will be there. The change in the absolute value of tbe property between the state 1 and state 2 is obtained from the difference between the  coordinates of the two points representing the states.

 

ΔP = P2 – P1 , and Δv = v2 –v1

 

Equation (1.1) shows that the properties do not depend on the path followed by the system during the change but depend only on the state. Thereby the property change do not dcpl’nd on the paths A, B, C but on end points (1 and 2). Such properties are known as point functions. Any variable is a property if it has a definite value at each state of equilibrium.