I just read the article on entropy of mixing and double checked a couple of independent sources and now understand that this formula for mixing presumes equal temperature of the two substances being mixed  Didnt know that before now  Thus the entropy of mixing refers to distribution of particles into a steadystate particle mix This is an entirely different use of the word entropy which does not involve thermodynamics  Learning new things here Nonetheless as to thermodynamic entropy it remains that dispersal of energy from warmer particles to cooler particles always represents an increase of entropy in a closed system consistently with the Second Law