In this course, we will now find out the reason for changes in matters (Chemical Principles II). The earlier course, Chemical Principles I, deals with the matter itself, and the understanding of it comes from quantum mechanics. However, for the change of matter, thermodynamics says the final word. The most critical quantity in thermodynamics is the entropy, and this course is all about understanding entropy and related thermodynamic potentials. Although classical thermodynamics was developed from observations and heuristic understanding, statistical thermodynamics provides a microscopic basis of it. In this course, a holistic approach covering three different approaches (classical, statistical, and postulate-based) of thermodynamics will be covered. The objective of this course is demystification the enigma of entropy.