Entropy (S) is a measure of the number of different ways that a system can store energy.
Entropy is related to probability as it is determined by the number of possible arrangements for a system.
Systems which have more arrangements available to them have higher entropy. Thus S(gas) > S(liquid) > S(solid)
The
Third Law of Thermodynamics states that the absolute entropy of any pure crystalline substance at 0 K is 0.
The entropy of a substance at temperature T is referred to as the absolute entropy (S°).
This is calculated by adding the entropy changes for the processes occurring on warming the substance from absolute zero to T.
If the
absolute entropy for all substances in a process are
known, the
entropy change for a process can be
calculated from these.
ΔS° = ΣnS°(products) - ΣnS°(reactants)
where n is the coefficient for that substance in the balanced equation