econd Law of Thermodynamics

econd Law of Thermodynamics - piston. Its volume will...

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econd Law of Thermodynamics An engine changes heat into work. In the engine of a car the heat is generated by the combustion of an air-gas mixture. The heat is used to expand the gas, and lift the piston. Although work can be completely changed into heat, the reverse is not true ( second law of thermodynamics ). The first form of the second law is: " It is not possible to completely change heat into work with no other change taking place " Let us look at an ideal gas confined by a piston in a volume V i . The gas is in contact with a heat reservoir with temperature T. The gas is permitted to expand by removing some weight of the
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Unformatted text preview: piston. Its volume will increase while its temperature remains constant. Since the internal energy of the gas only depends on its temperature, the internal energy of the gas will not change. From the first law of thermodynamics we conclude that This shows that we have converted all extracted heat into work. However, in the process we have also changed the state of the gas. Its volume and pressure have changed. In order to return the gas to its internal state we need to do work and extract heat from the system. In that case, the net work and heat will be zero....
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This document was uploaded on 11/25/2011.

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