The Second Law: Thermodynamic Temperature and Entropy

Abstract

In Programme 1 we said that in studying Thermodynamics we have to take a macroscopic view. This is because some of the forms of energy we have to consider can only be treated in terms of macroscopic ideas. Internal energy of a fluid depends on the translational and vibrational energy of countless myriads of tiny molecules, and we can only get a picture of the state of that fluid by using the overall concepts of temperature and pressure. Since internal energy is that mode of energy directly affected by a heat interaction, heat itself is an energy transfer that depends on random molecular activity, which again can only be viewed with macroscopic ideas. Even though similar macroscopic ideas, such as force (being pressure × area) are used describe a work transfer, heat and work, as interactions at a system boundary, are fundamentally different.