Exploring Entropy: Disorder and Probability in Nature

1. Is this your room/ Then you already know about entropy

2. Using a simple approach, Define entropy as a measure of disorder. A system (such as a room) is in a state of high entropy when its degree of disorder is high. As the order within a system increases, its entropy decreases.

3. A system (such as a room) is in a state of high entropy when its degree of disorder is high. For better or for worse, nature 'likes' chaos, disorder, high entropy... In fact, much of our life consists in fighting this disorder!

4. This can be explained in terms of probabilities. Disordered states are simply more likely to exist (or emerge) than ordered states. The spontaneous direction of change is from a less probable to a more probable state, as illustrated above.

5. The perfect blend • Why do hydrocarbons mix? Read story Pg 32 • Mixing leads to an increase of entropy. • Entropy: the amount of disorder or randomness in a system. • You need to read CI 4.3 Entropy

6. In general • Gases have higher entropies than liquids. • Liquids have higher entropies than solids. • Substances have higher entropies if their molecules contain heavier atoms and larger number of atoms. There are more ways of arranging particles in a gaseous state than a solid state

7. Examples • Ar has higher entropy than Ne as Ar molecules are larger. • C8H18(l) has higher entropy than C5H12(l) as complex molecules have higher entropy than simple ones. • Br2(g) has higher entropy than Br2(l) as gases have higher entropies than liquids since gases have more ways of being arranged

8. Entropy (CI 4.3) • Liquids mix because there are more ways of being mixed than unmixed. • i.e. disorder increases. • Note that: not all liquids mix; e.g. water does not mix with oil, because the forces of attraction between water molecules are stronger than the forces of attraction between oil molecules •  they do not mix They are immiscible

10. Now you need to do Problems for CI 4.3