Lecture 20 uses the Carnot Cycle to introduce entropy and the second law of thermodynamics. It covers material from Chapter 18, Chemical Thermodynamics The power point presentation can be downloaded from this file. Except where noted the images are from the text. You are free to change the presentation in any way. If you wish I would appreciate the opportunity of including your version with attribution in this Libretext. My Email address is jhalpern and I am at howard.edu.