The Chemical Potential and Other Partial Molar Quantities

8 The Chemical Potential and Other Partial Molar Quantities 

So far, we have focused on changes in systems that are measured in terms of the system s physical variables, like pressure and temperature and volume and the like. But in chemical reactions, substances change their chemical form. We need to begin to focus on the chemical identity of a material and how it might change during the course of a process. 

It has been assumed that the number of moles, n, of a substance has remained constant in all of the changes considered so far. All of the partial derivatives should also have an n subscript on the right side to indicate that the amount of material remains constant for example, dUldV)j- . However, there is no reason that we can t consider a derivative with respect to amount, n. 

Unless otherwise noted, all art on this page is Cengage Learning 2014. 

Because of the importance of the Gibbs energy in spontaneity considerations, the majority of derivatives with respect to n concern G. The chemical potential of a substance, /x, is defined as the change in the Gibbs energy with respect to amount at constant temperature and pressure  

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