Is this your room/

Then you already know about entropy

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.

For better or for worse, nature 'likes' chaos, disorder, high entropy... In fact, much of our life consists in fighting this disorder!

A system (such as a room) is in a state of high entropy when its degree of disorder is high.

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.

220 ways to arrange?

In general

• Gases have higher entropies than liquids.

• Liquids have higher entropies than solids.

Also …

• Entropy is greater for larger atoms.

• Entropy is greater for molecules with more atoms.

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

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

On to CI 4.4

• AS – entropy is a measure of the number of ways particles can be arranged.

• A2 – entropy is a measure of the number of ways quanta (packages of energy) can be arranged.

What happens to electrons?

1

234

• Electrons absorb quanta of energy

• Electrons are excited

• Electrons move to higher energy level

• E = h v

Molecules are made of more than one atom but they still have

electrons.• Electronic

transitions

Vis + UV

Molecules move !

There are vibrational energy levels as well as electronic energy level ..

I.R.

There are rotational energy levels as well as electronic energy level ..

microwave

• Electronic transitions

Vis + UV

• Rotational transitions

• Vibrational transitions

Microwave

I.R.

E V R T

E V R T

On to CI 4.4

• AS – entropy is a measure of the number of ways particles can be arranged.

• A2 – entropy is a measure of the number of ways quanta (packages of energy) can be arranged.

4 quanta – 2 molecules

Molecule 1 Molecule 2

0 4

1 3

2 2

3 1

4 0

5 ways

6 quanta – 2 molecules?More quanta

Molecule 1 Molecule 2

5 7 more ways

4 quanta – 2 molecules

Molecule 1 Molecule 2

0 4

1 3

2 2

3 1

4 0

5 ways

4 quanta – 3 molecules

Molecule 1 Molecule 2 Molecule 3

Moremolecules

5 15More ways

On to CI 4.4

• AS – entropy is a measure of the number of ways particles can be arranged.

• A2 – entropy is a measure of the number of ways quanta (packages of energy) can be arranged.

• Entropy greater if more quanta (heat it)

• Entropy greater if more molecules

Bigger atoms/molecules have more entropy?

E V R T

E V R T

E V R T