ETH Polymer Physics seminar


2010-06-30
10:15 at HCI J 574

How to (not) teach the second law

Henning Struchtrup

Department of Mechanical Engineering, University of Victoria

When introducing the second law, most (engineering) textbooks follow the historical development and base the arguments on Carnot cycles. Obviously, this path requires discussion of property relations and processes, all based solely on the 1st law, before the 2nd law can be tackled. Two main problems arise from this: (a) Entropy and 2nd law are introduced relatively late, so that in an introductory course students have little time to get familiar with these important concepts. (b) After one has the 2nd law, one has to go back and discuss all processes again, this time with entropy included. In this talk I present an alternative introduction of entropy and the 2nd law for teaching purposes, which can be done early in a course. With this the 2nd law and entropy are available early on, and can be used for the discussion of cycles and processes from the beginning. The 2nd law is introduced based on the following observations/postulates for closed systems: (i) An isolated system will, after a while, assume a stable and unique equilibrium state. (ii) Energy can be transferred only by heat and work (the 1st law). (iii) The state of a closed system can be changed only through exchange of heat and work. (iv) Heat goes from hot to cold by itself, but not vice versa. (v) There is no direction restriction for work transfer (one can use gears and levers).


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