TABLE OF CONTENTS The first and second laws of thermodynamics provide a basis for constructing relations among the macroscopic properties of physical systems. These properties include temperature, pressure, volume, energy, specific heat, compressibility, and so forth. In a one-component, one-phase system, two variables (e.g., temperature and pressure) are enough to define the thermodynamic state. All other properties are then determined by the equations of thermodynamics. For systems in equilibrium, the thermodynamic state is defined by a number of macroscopic properties determined by the phase rule given by (1.14.12).
The thermodynamic parameters of a system are of two kinds: mechanical and nonmechanical. Mechanical variables are those quantities that can be interpreted in mechanical terms, such as energy and internal pressure. Non-mechanical variables are those that have no analog in mechanics and are peculiar to thermodynamics. These include temperature and entropy.
Thermodynamic quantities can also be classified as being intensive or extensive. Intensive parameters are those that are independent of the size of the system, such as temperature, pressure, and concentration of components. Extensive parameters are those that are directly proportional to the amount of matter in the system, such as volume, energy, and heat capacity.
Also, it is useful to distinguish between the properties of the system and external parameters. The external parameters define the conditions under which the system exists and its interaction with the environment. These include such quantities as external fields (gravitational, electric, magnetic), the pressure of a movable piston, and the temperature...
