Quick thermodynamics primer

The thermodynamic properties of a system (pure substance or mixture) are numerous, but experiments have shown that a limited number of these quantities suffice for the knowledge of a system and for the determination of all the other properties. These quantities are called state quantities, all the others being state functions (that is functions of state quantities) which by nature are extensive. The number of state variables is characteristic of the studied system, the choice of state variables among the state quantities being largely arbitrary. 

In order to describe the properties of a homogeneous fluid, three state variables are necessary among the following quantities temperature (T), pressure (P), volume (V) and number of moles (n), the fourth being a state quantity. There is a relationship between these four quantities which can be the ideal gas equation or Van der Waals gas equation. 

1 In thermodynamics, an extensive quantity characterizing a physical system is proportional to the size of this system, the system being assumed at equilibrium and homogeneous. During the reunion of two systems, the value of the quantity is equal to the sum of the values of this quantity for the two disjointed systems. 

Classical thermod5Tiamics defines several state fiinctions  

Given an extensive quantity of a mixture of p components. In the case 

---