Entropy and Second Law

This lecture introduces entropy and its relation with the second law of thermodynamics, showcasing examples of entropy calculations for reversible and irreversible processes. The instructor demonstrates the calculation of entropy changes for various scenarios, such as a nearly reversible liquefaction process, heat exchange between two bodies at different temperatures, and the irreversible Joule expansion. Through these examples, the lecture emphasizes the increase in total entropy for irreversible processes, illustrating the concept with practical applications like a refrigeration cycle. The discussion concludes with a detailed analysis of a refrigeration cycle, highlighting the importance of work input and heat exchange in maintaining system equilibrium.