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What is entropy?

Measure of disorder/randomness of system

What is the symbol and units for entropy?

Symbol: S

Units: J/K (joules per kelvin).

Rank the entropy of phases from least to greatest.

Solids < Liquids < Gases

spontaneity (scientific entropy def)

Possible configurations in a system

configurations => position (more ways can break - more entropy) + energy

spontaneity (analogy)

• breaking an egg

• saturday vs tuseday 8pm library population (tues = high S vs saturday = low S)

entropy (scientifically)

of possible microstates (specific configurations of position -> where they are & energy -> how fast they are moving); more microstates mean higher entropy;

Even if a system looks the same on the outside (same temperature, pressure, etc.), the particles inside can be arranged differently.

second law of thermodynamics

The entropy of the Universe is always increasing. The total change in entropy of the Universe is always positive.

gas

Gases have the most kinetic & potential energy → most entropy

Arrangement of particles: furthest apart → high PE

Freedom of motion: greatest (almost no limitation) → high KE

higher entropy can also be caused by…

• more atoms

• higher amt of moles

(more microstates + heavier)

What happens to entropy during melting and vaporization?

Entropy increases (S_{sys} > 0)

What happens to entropy during freezing and condensation?

Entropy decreases (S_{sys} < 0)

How does molecular complexity affect entropy?

More complex molecules have greater entropy due to more vibrations and microstates.

If a reaction is exothermic (H{sys} < 0), what happens to S{surr}?

S_{surr} > 0 (entropy of surroundings increases).

What is the formula for entropy change of the Universe?

S{uni} = S{sys} + S_{surr}

What defines a spontaneous process?

A process that increases the entropy of the Universe (S_{uni} > 0)

Give an example of a spontaneous process.

Combustion — once started, it continues until completion.

impacts on entropy

• volume

• quantity

• time

freezing

exothermic (heat is leaving system)

melting

endothermic

S{uni}=S{sys}+S_{surr}

S{sys} and S{surr} are opposite in sign, the sign of S_{uni}, which determines spontaneity, depends on the temperature of the system.

What happens to spontaneity at high temperature when S{sys} and S{surr} have opposite signs?

At high temperature, the magnitude of S{sys} is greater than S{surr}, so S_{sys} dominates.

If S{sys} < 0 and S{surr} > 0, then S_{uni} < 0 → not spontaneous.

If S{sys} > 0 and S{surr} < 0, then S_{uni} > 0 → spontaneous.

What happens to spontaneity at low temperature when S{sys} and S{surr} have opposite signs?

At low temperature, magnitude of S{surr} is greater than S{sys}, so S_{surr} dominates.

If S{sys} < 0 and S{surr} > 0, then S_{uni} > 0 → spontaneous.

If S{sys} > 0 and S{surr} < 0, then S_{uni} < 0 → not spontaneous.

How does the sign of S_{uni} determine spontaneity?

S_{uni} > 0: Entropy of the universe increases → spontaneous

S_{uni} < 0: Entropy of the universe decreases → not spontaneous

Hsys < 0     →     Hsurr > 0     →     Ssurr > 0 

System lost energy.

Surroundings gained energy.

Surroundings increased in entropy.

E.g exothermic reactions

Hsys > 0     →     Hsurr < 0     →     Ssurr < 0

System gained energy.

Surroundings lost energy.

Surroundings decreased in entropy.