Molecular Kinetic Interpretation of Entropy

Atomic Disorder So what is this entity that flows through matter and, depending upon how much is contained in it, causes it to seem warm or hot to the hand For more than two hundred years, one has attempted to explain thermal phenomena by the movements of atoms. The image is as follows The warmer a body is, the more intensely and randomly the atoms oscillate, spin, and swirl—so the idea, the greater the agitation and the worse the atomic disorder. 

In the particle view, the quantity called entropy is a measure of 

The same holds for the world of atoms (Fig. 3.7). Not only disorder in the type and distribution of atoms, but also disorder in their motion, which can be expressed in how agitated they are, makes an important contribution to entropy. In this sense, the atoms in a hot gas are similar to children romping in the schoolyard. Motions are completely free and without order, and therefore the agitation, meaning the disorder concerning motion, is great. The atoms of a crystal, in contrast, can be compared to tired pupils in a school bus. Motion is more or less limited to fixed locations, so the disorder and agitation stay small. 

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