Behavoir of a thermodynamic system

The behavior of the system depends upon the interaction of energy with or without mass transfer across the boundary. Every system has certain characteristics by which its physical conditions may be described. Such behavior/characteristics of a system are called the properties of the system. There are 8 (eight) properties describing the behavior of a system. They are pressure, temperature, volume, entropy, internal energy, enthalpy, Gibbs function and Helmholtz functions. Pressure, temperature and volume are measurable properties and they are also known as physical properties (also known as macroscopic properties). Other properties are derived properties (they can not be measured directly). In sense of thermodynamics, pressure is always expressed in terms of absolute pressure and temperature is expressed in Kelvin.

When all the properties of a system have definite values, the system is said to exist in a definite state. State of a thermodynamic system can be indicated in a diagram with properties as coordinates.

Intensive and extensive properties

Thermodynamic properties can be divided into 2 (two) general classes such as intensive and extensive properties. An intensive property, is a physical property of a system that does not depend on the system size or the amount of material in the system. By contrast, an extensive property of a system does depend on the system size or the amount of material in the system. According to the definitions, density, pressure and temperature are intensive porperties and volume, internal energy are extensive properties.

Symbols for representing properties: Extensive properties are symbolized by upper case (capital) letter such as V (volume), KE (kinetic energy), PE (potential energy), etc. Intensive properties are symbolized by lower case letters such as v (specific volume), ke (specific kinetic energy), e, u (specific internal energy), h (specific enthalpy), etc. Mole based properties are symbolized by lower case letters with overbars. For example , , , and are molar specific voulme, molar specific energy, molar specific kinetic energy and molar specific potential energy respectively.

Exceptions: Temperature (intensive), mass (extensive), and number of moles (extensive). The use of symbols for temperature, mass and moles are traditional.