The statistical mechanical interpretation of entropy

Entropy can be interpreted in terms of the number of distinct ways in which a given overall situation can occur, or the number of ways of arranging the system  

Although there are some cmcial distinctions, particularly for gas phase systems where the correlation is only partial, there is for electrolyte solutions a correlation between order/ disorder and entropy. It is this correlation which has proved to be very fruitful for the interpretation of AS  

If a system changes from one which is ordered to a less ordered system, then the number of ways of arranging the system must increase, and so the randomness wiU increase leading to an increase in entropy. 

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For those who are familiar with the statistical mechanical interpretation of entropy, which asserts that at 0 K substances are nonnally restricted to a single quantum state, and hence have zero entropy, it should be pointed out that the conventional thennodynamic zero of entropy is not quite that, since most elements and compounds are mixtures of isotopic species that in principle should separate at 0 K, but of course do not. The thennodynamic entropies reported in tables ignore the entropy of isotopic mixing, and m some cases ignore other complications as well, e.g. ortho- and para-hydrogen. 

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