Entropy, Probability, and Disorder

After the expansion, the probability (pfinal) of finding all No molecules in the final volume Vi + V2 must be 1.0. The ratio of these two probabilities is 

We will see in Chapter 10 that the expression for the entropy change in this expansion process is 

The number of molecules divided by the number of moles is Avogadro s number, Na, so that 

Thus there seems to be a relationship between entropy and probability. In the example mentioned above where Vi/(Vi + V2) = 0.5, (6.2) becomes, for one mole of gas, 

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