Question

what does the symbol mu represent in thermodynamics?

Answer 1

The symbol μ' in thermodynamics represents the chemical potential. It is same as the Gibb's free energy bur it it partial derivative of dG with respect to the amount of species.This is like the potential energy which is released or absorbed during the chemical reaction.
$$\begin{gathered} dG=-SdT+VdP+\underset{i=1}{\overset{n}{\sum {\mu }_{i}d{N}_i}} \\ {\mu }_i=(\frac{\partial G}{\partial N_i}{)}_{T,P} \end{gathered}$$