Second Law of Thermodynamics and Entropy

by Pearl Ruparel

Second Law of Thermodynamics

Thermodynamics is a huge area of physics that deals with study of effects of work, heat, and energy on a system. It is concerned with large scale observations. There is zeroth law, first law, and second law of thermodynamics. The zeroth law involves simple definition of thermodynamic equilibrium while the first law deals mainly with kinetic and potential energy and transfer of heat and internal energy while introducing enthalpy which leads to second law of thermodynamics. The second law of thermodynamics stipulates that the total entropy of a system plus its environment can not decrease; it can remain constant for a reversible process but must always increase for an irreversible process. Entropy is described as measure of disorder in a closed system/ thermal energy not available to do work.

A Mathematical Model

Entropy is a state variable whose change is defined for a reversible process at T where Q is the heat absorbed. It can be calculated for a reaction using the equation \deltaS = Q / T where Q is the heat absorbed for temperature T.

A Computational Model

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Examples

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History

According to philosopher of science Thomas Kuhn, the second law was first put into words by two scientists, Rudolph Clausius and William Thomson (Lord Kelvin), using different examples, in 1850-51. Clausius invented the term in 1865. He had noticed that a certain ratio was constant in reversible, or ideal, heat cycles. The ratio was heat exchanged to absolute temperature. Clausius decided that the conserved ratio must correspond to a real, physical quantity, and he named it "entropy".

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See also

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