Generalized forces and coordinates

When a mass of any substance is subject to some physical change, certain properties—mass, chemical composition—remain fixed and invariable, while other properties—temperature, pressure, volume—vary. When the value these variables assume in any given condition of the substance is known, we are said to have a complete knowledge of the state of the system. These variable properties are not necessarily independent of one another. We have just seen, for instance, that if two of the three variables defining the state of a perfect gas are known, the third variable, can be determined from the equation pv = BTt 

I is said to be a dependent variable, the other two, independent vari- 

in order that we may possess a knowledge of some systems, say gaseous nitrogen peroxide, not only must the variables given by the gas equation 

We know that the dissociation of N204 into 2N02 depends on the volume, temperature and amount of N02 present in the system under consideration. At ordinary temperatures 

In general, if a system contains m dependent and n independent variables, say 

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K the zero-point atomization energy, the heats of formation and their dependences on temperature and on the generalized forces and coordinates are known, all the most important thermodynamic functions and their temperature dependences can be determined. 

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