This lecture covers the second law of thermodynamics, focusing on the concept of entropy. It explains the distinction between heat and work at a microscopic level, the irreversibility of the transformation from order to disorder, and the maximum efficiency theorem. The lecture introduces the extensive state function entropy (S) and the thermodynamic temperature (T). It discusses the variation of entropy between two states, emphasizing its independence of the path taken. The lecture also explores entropy in different systems: stationary, equilibrium, and isolated. It concludes with a discussion on the creation of internal entropy and the concept of thermodynamic equilibrium. Various questions related to thermodynamic processes and the limitations imposed by the second law are addressed.