Thermodynamics

Thermodynamics (Greek: thermos = heat and dynamis = power) is the physics of heat, work, enthalpy, and entropy changes in relation to the spontaneity of processes. In origins, thermodynamics is the study of engines. Prior to 1698, with the invention of the Savery Engine, horses were used to "power" pulleys, attached to buckets, which lifted water out of flooded salt mines in England. In the years to follow, more variations of steam engines were built; as the Newcomen Engine, and later the Watt Engine. In time, these early engines would eventually be utilized in place of horses. Thus, each engine began to be associated with a certain amount of "horse power" depending upon how many horses it had replaced! The main problem with these first engines was that they were slow and clumsy, converting less than 2% of the input fuel into useful work. In other words, large quantities of coal (or wood) had to be burned to yield only a small fraction of work output. Hence the need for a new science of engine dynamics was born.

Thermodynamic parameters

The parameters used to describe the state of a system generally depend on the exact system under consideration, and the conditions under which that system is maintained. The most commonly considered parameters are:

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:Mechanical parameters:

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:* Pressure: p

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:* Volume: V

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:Statistical parameters:

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:* Temperature: T

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:* Entropy: S

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:Two more parameters can be considered for open systems:

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:* Number of particles, N, of each component of the system

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:* Chemical potential, mu, of each component of the system

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The mechanical parameters listed above can be described in terms of fundamental classical or quantum physics, while the statistical parameters can be understood only in terms of statistical mechanics.

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In most applications of thermodynamics, one or more of these parameters will be held constant, while one or more of the remaining parameters are allowed to vary. Mathematically, this means the system can be described as a point in n-dimensional space, where n is the number of parameters not held fixed. Using statistical mechanics, combined with the laws of classical or quantum physics, equations of state can be derived which express each of these parameters in terms of the others. The simplest and most important of these equations of state is the ideal gas law

Related Topics:
Statistical mechanics - Classical - Quantum - Equations of state - Ideal gas law

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:pV=nRT ,

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where R is the universal gas constant.

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and its derived equation:

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:pV=NkT ,

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where k is the Boltzmann constant.

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Pressure cannot be varied in experiment. Any changes in pressure are caused by changes in the number of molecules, the temperature, or the volume of the gas. In an experiment, you cannot make pressure the independent variable. The pressure a gas exerts on a container is a function of the number of molecules, the temperature (kinetic energy), and the volume of the container. It can be useful to think of pressure as a dependent variable which is the function of n, T, and V such that

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:p=(nRT)/V ,

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