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Unformatted text preview: 5/18/2004 H133 Spring 2004 1 Chapter 4 We have spent some time developing the model of ideal gases and have learned a number of important concepts. However, we still have not learned much regarding why certain processes are irreversible. We are getting closer to that holy grail. But we need to define some more terms In this chapter we go through all these points and by the end we will have all the pieces to understand why some processes are irreversible . Macrostate: We defined this earlier for an ideal gas Most (not all) combinations of three of the following served to describe the macroscopic properties of an ideal gas: o U, T, P, V, N, M, along with the composition. For other things like liquid and solids we will have a similar set of variables that define the macroscopic state of the substance. When we define an Einstein Solid in a few minutes we will see that we can use the internal energy U and the number of molecules, N to define the state. 5/18/2004 H133 Spring 2004 2 Microstates Microstate: The microstate of a system (gas, solid, or liquid) is defined as the set of quantities which defines the state of every molecule in the system. One option: We could also think about this as being the set of quantum numbers that describe each state of each particle. (This is what we will do for the Einstein Solid.) A quantum in a 1d box If we extend this idea to 3dimensions, Note that for N molecules we need In practice, it is impossible to determine the microstate of an object. Think about a gas containing 10 23 moleculeswe cannot possibly determine all the individual states of these particles. o Important Point: For any given macrostate there is a HUGE number of microstates. Think about an ideal gas with U, T, N The total internal energy U is in the K (monatomic) but this can be shared in many different ways. Given a Microstate we could get the Macrostate . 5/18/2004 H133 Spring 2004 3 We could try develop some of the concepts of microstates, macropartions, etc. in terms of ideal gases but there is a simpler model that we can use. Einstein Solid. Einstein developed a very simple model for solids in order to investigate some of these concepts of statistical mechanics. Model: The oscillations are The picture is a lattice of atoms attached by springs....
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This note was uploaded on 06/03/2011 for the course H 133 taught by Professor Furnstahl during the Spring '11 term at Ohio State.
 Spring '11
 Furnstahl
 Quantum Physics

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