This lecture covers the experiments of Boyle-Mariotte, Charles, and Gay-Lussac, the concept of absolute temperature, and Avogadro's hypothesis. It explains the relationship between pressure, volume, temperature, and the number of moles in ideal gases, as well as the significance of Avogadro's number in quantifying the amount of gas. The lecture also delves into the laws governing ideal gases and the constant properties of gases. Furthermore, it explores the concept of a perfect gas and its behavior under different conditions, providing examples and calculations to illustrate these principles.