By Sunil Bhardwaj

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The disorder or chaos of a system is expressed in terms of a function called entropy of the system. e.g. the ions of common salt in solid state are held together in a regular manner but when it is dissolved in water ions become free to move anywhere in the water, and as a result order is distroyed. Thus, greater the disorder of a system the greater is its entropy.

Therefore entropy change ds is defined as The ratio of heat absorbed reversibly with the absolute temperature. or $$ ds = \frac { { q }_{ rev } }{ T } \qquad ....(1) $$ The units for entropy is Joules/Kelvin (J/K).