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Standard Entropy Values3/20/2021
The values found in the table are normally those for 298K, and are expressed in units of latexfrac textJtextK cdot textmolelatex.Some typical standard entropy values for gaseous substances include.Entropy, however, measures not energy itself, but its dispersal among the various quantum states available to accept it, and these exist even in pure elements.For the noble gases, this is a direct reflection of the principle that translational quantum states are more closely packed in heavier molecules, allowing them to be occupied.
The entropies of the diatomic and polyatomic molecules show the additional effects of rotational quantum levels. Although both diamond and graphite are types of carbon, their entropies differ significantly. Graphite, which is built up of loosely-bound stacks of hexagonal sheets, soaks up thermal energy twice as well as diamond. ![]() For example, sodium, which can be cut with a knife, has almost twice the entropy of iron, which cannot be easily cut. These trends are consistent with the principle that the more disordered a substance, the greater its entropy. ![]() According to the second law of thermodynamics, a spontaneous reaction always results in an increase in total entropy of the system and its surroundings.
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