Explain entropy and its relationship to phase change and number of moles

Here's what I get.    

Explanation:

What is entropy?

Entropy (S) is often described as a measure of the disorder in a system, but it is really a measure or the number of microstates (W).

A microstate is a specific configuration of the locations of particles and the way that energy is distributed among them.

Entropy is a measure of the degree of the spreading of energy within a system. The more ways that energy can be distributed, the greater the entropy.

Entropy and phase changes

In the solid phase, the particles are in fixed locations and can vibrate slightly about these locations. The number of microstates is relatively small.

If you add energy and convert the solid to a liquid, the particles can slide past each other. The particles have more freedom of motion, so the energy is distributed in more ways. There are more microstates, so S(liquid) > S(solid).

If you add more energy and convert the liquid to a gas, the particles can move in all directions, and the number of microstates (and also S) increases enormously.  

Entropy and number of moles

The more particles you have, the more microstates (ways to distribute the energy) there are.

However, the entropy of gaseous particles far outweighs that of those in solids or liquids.

That's why, when you are asked to predict the sign of ΔS for a reaction, all you need do is calculate the change in the number of moles (Δn) of gases.

If the products contain more moles of gases, ΔS > 0. If the products contain fewer moles of gases, ΔS < 0.

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