Chapter 12 (I)

Chapter 12 (I) - Chapter 12. Statistical Thermodynamics...

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Chapter 12. Statistical Thermodynamics 12.1 System and ensembles Introduction. Statistical mechanics deals with the following problem: we have a system , that is, the part of the physical world, in which we are interested. About this macroscopic system, we know certain information from measurements or observations, e.g., V, M, T. We call these as the equilibrium properties of the system. Now, we want to get a microscopic picture of the system, that is, a picture of the (mechanical) behaviors of the microscopic particles that make up the system; they can be molecules, atoms, electrons or photons, etc. V M T
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From the classical mechanics, we know that particles can be described by the mechanical states. In the present case, however, we do not know exactly what the mechanical states all the N particles are in the system. But we know that each possible state has its own probability of being occupied. Thus, one construct an ensemble to represent the system, to find the total probability of the available states be occupied by all the particles. This probability distribution for various states is subject to the equilibrium-state conditions. There are three sets of equilibrium conditions, giving 3 types of ensembles, as detailed below.
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To represent a completely isolated system consisting of N particles contained in a volume V. The system is completely described by N, V and E, which are constants.
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Chapter 12 (I) - Chapter 12. Statistical Thermodynamics...

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