10.3 - entropy and the 2nd law

MATTER IS ENERGY.

ENERGY IS INFORMATION.

EVERYTHING IS INFORMATION.

PHYSICS SAYS THAT

STRUCTURES...

BUILDINGS, SOCIETIES,

IDEOLOGIES... WILL SEEK

THEIR POINT OF LEAST

ENERGY.

THIS MEANS THAT

THINGS FALL.

THEY FALL FROM HEIGHTS

OF ENERGY AND

STRUCTURED INFORMATION

INTO MEANINGLESS,

POWERLESS DISORDER.

THIS IS CALLED

ENTROPY.

Entropy (S) = a measure of randomness or disorder

Entropy

It’s just a measure of disorder

Physics classrooms are full of Entropy!

Entropy and your bedroom

Low Entropy High Entropy

No matter what we say or try, the entropy of the universe is increasing!

The molecules in the solid are in a much more restricted or ordered state so they have low entropy.

Entropy increases when melting.

Entropy decreases when freezing

What happens to entropy when a machine does work?

ΔS ↓

ΔS ↑

Refrigerators

Room

ΔS ↓

ΔS ↑

The heat pump in the fridge does work to reduce the entropy inside it.

The entropy of the room increases by more.

What happens to the temperature of the room?

The temperature of the room increases .

Entropy Increases with...• Melting (fusion) Sliquid > Ssolid

• Vaporization Sgas > Sliquid

• Heating ST2 > ST1 if T2 > T1

• Dissolving (usually) Ssolution > (Ssolvent + Ssolute)

• Molecular complexity more bonds, more entropy

• Atomic complexity more e-, protons, neutrons

Entropy Curve

Solid GasLiquid

SEntropy

Temperature (K)0

0

fusion

vaporization

The Statistics of Entropy

Another way to think about entropy is that being disordered is just more likely.

It’s just chance

A box containing air molecules, divided in two compartments with a hole in the dividing wall. Since there are many more molecules in the left compartment, there will also be many more molecules crossing the divide from left to right.

The second law of thermodynamics states that in an isolated system the entropy will increase. In the statistical definition of entropy according to Boltzmann, this means that the system will evolve to its most probable state.

Entropy, Marble Example

• Suppose you have a bag with 50 red marbles and 50 green marbles

• You draw a marble, record its color, return it to the bag, and draw another

• Continue until four marbles have been drawn

• What are the possible results and what are their probabilities?

Entropy, Marble Example, Results

• The most ordered are the least likely• The most disorder is the most likely

Entropy & Time

Because systems move from order to disorder, time has a direction.

Which came first?

Entropy and Life

Life is an entropy reducerDoes this break the second law of thermodynamics?