a B: The second Law of Thermodynamics [AW 42-50: VN Chapter 5; VwB&S-6.3, 6.4, Chapter 7 1. B. Concept and statements of the Second law why do we need a second law?) The unrestrained expansion, or the temperature equilibration of the two bricks, are familiar processes. Suppose you are asked whether you have ever seen the reverse of these processes take lace? Do two bricks at a medium temperature ever go to a state where one is hot and one is cold? will the gas in the unrestrained expansion ever spontaneously return to occupying only the left side of the volume? Experience hints that the answer is no. However, both these processes, unfamiliar their occurrence. There the mpatible with the first law. In other words the first law does not prohibit though they may be, are co lus must be some other"great principle"that describes the direction of natural processes, that tells us which first law compatible processes will not be observed. This contained in the second law. Like the first law, it is a generalization from an enormous amount of observation There are several ways in which the second law of thermodynamics can be stated. Listed below are three that are often encountered. As described in class(and as derived in almost every thermodynamics textbook), although the three may not appear to have much connection with each other they are equivalent 1)No process is possible whose sole result is the absorption of heat from a reservoir and the conversion of this heat into work. [Kelvin-Planck statement of the second law] Q System w This is not possible 2) No process is possible whose sole result is the transfer of heat from a cooler to a hotter Clausius statement of the second law Q For T<T2, this is not possible 1B-11.B: The Second Law of Thermodynamics [IAW 42-50; VN Chapter 5; VWB&S-6.3, 6.4, Chapter 7] 1.B.1 Concept and Statements of the Second Law (Why do we need a second law?) The unrestrained expansion, or the temperature equilibration of the two bricks, are familiar processes. Suppose you are asked whether you have ever seen the reverse of these processes take place? Do two bricks at a medium temperature ever go to a state where one is hot and one is cold? Will the gas in the unrestrained expansion ever spontaneously return to occupying only the left side of the volume? Experience hints that the answer is no. However, both these processes, unfamiliar though they may be, are compatible with the first law. In other words the first law does not prohibit their occurrence. There thus must be some other “great principle” that describes the direction of natural processes, that tells us which first law compatible processes will not be observed. This is contained in the second law. Like the first law, it is a generalization from an enormous amount of observation. There are several ways in which the second law of thermodynamics can be stated. Listed below are three that are often encountered. As described in class (and as derived in almost every thermodynamics textbook), although the three may not appear to have much connection with each other, they are equivalent. 1) No process is possible whose sole result is the absorption of heat from a reservoir and the conversion of this heat into work. [Kelvin-Planck statement of the second law] Q System T2 W This is not possible T1 2) No process is possible whose sole result is the transfer of heat from a cooler to a hotter body. [Clausius statement of the second law] Q T2 T1 For T1 < T2 , this is not possible Q 1B-1