Gibbs Free Energy Sites

http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch21/gibbs.php

https://www.chem.tamu.edu/class/majors/tutorialnotefiles/gibbs.htm

https://www.khanacademy.org/science/physics/thermodynamics/v/gibbs-free-energy-and-spontaneity