Second Law of Thermodynamics

Topics: Thermodynamics, Entropy, Heat Pages: 3 (1022 words) Published: April 15, 2013
The first law of thermodynamics states that a certain energy balance will hold when a system undergoes a change of state or a thermodynamic process. But it does not indicate whether that change of state or the process is at all feasible or not. It is the second law of thermodynamics which provides the criterion as to the probability of various processes through the statements of Clausius that ‘’Heat does not pass from a body at low temperature to one at high temperature without an accompanying change elsewhere’’ and Kelvin that ‘’No cyclic process is possible in which heat is taken from a hot source and converted completely into work’’. The aim of this essay is to prove if there equivalence between these two statements and it will be achieved by analysing them. (Nag,2008) The Kelvin statement of the second law of thermodynamics considers that is impossible to be constructed a cyclically operating device that it absorbs energy as heat from a single thermal reservoir and performs an equivalent amount of work without producing no other effect. With other words, Kelvin statement implies that it is not possible to be constructed an engine which, while operating cyclically, absorbs a certain amount of energy as heat from a high temperature reservoir (source) and converts all of it into work. The only option is then that the engine converts part of the energy it receives as heat into work and the rest is rejected to an another thermal reservoir which its temperature is less than the temperature of the source. Then for a heat engine are needed at least two thermal reservoirs, one of high temperature (source) from which the working fluid receive the energy as heat and an another of low temperature (sink) to which the working fluid rejects the energy as heat. In this way, it is considered that no heat engine can have thermal efficiency 100% but its efficiency would always be lower than 100%. As concerns the Clausius statement of the second law of the thermodynamics, it is...
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