# Partial derivatives in thermodynamics

1. Mar 1, 2009

### maxBrunsfeld

in basic multivariate calculus, i never learned about differentiating functions of multiple variables which are also functions of each other. i.e.

$\frac{d}{d x_1} \left[ f(x_1, x_2, x_3) \right]$

where $x_1 = g(x_2, x_3)$

studying thermodynamics right now, i'm encountering into expressions like

$\mu = - \left(\frac{\partial U}{\partial S} \right)_{N,V} \left( \frac{\partial S}{\partial N} \right)_{U,V}$

where some particular variables are held fixed, but others are not. i'm wondering if there are formal theorems relating to partial derivatives like these or if you guys have any knowledge specifically relating to them.

2. Mar 1, 2009

### Staff: Mentor

All the thermodynamics textbooks that I've seen, spend some time discussing them early on.