mathematical epidemiology by adding components and elementary reactions. Individuals in human or animal populations unlike molecules in an ideal solution do not mix homogeneously. There are some disease examples in which this non-homogeneity is great enough such that the outputs of the classical SIR model and their simple generalizations like SIS or SEIR, are invalid. For these situations, more sophisticated compartmental models or distributed reaction-diffusion models may be useful. In sociophysics Sociophysics uses tools and concepts from physics and physical chemistry to describe some aspects of social and political behavior. It attempts to explain why and how humans behave much like atoms, at least in some aspects of their collective lives. The law of mass action (generalized if it is necessary) is the main tool to produce the equation of interactions of humans in sociophysics. See also Chemical equilibrium Chemical potential Equilibrium constant Reaction quotient References Further reading Studies Concerning Affinity. P. Waage and C.M. Guldberg; Henry I. Abrash, Translator. "Guldberg and Waage and the Law of Mass Action", E.W. Lund, J. Chem. Ed., (1965), 42, 548-550. A simple explanation of the mass action law. H. Motulsky. The Thermodynamic Equilibrium Constant History of chemistry Equilibrium chemistry Chemical kinetics Jacobus Henricus van 't Hoff