Unit 9 time to shine

Entropy

Entropy

thermodynamic function that describes the number of arrangements (positions, microstates, and/or energy levels) that are available to a system existing in a given state.

+ ΔS, positive entropy change

entropy of the system increases (favored)

-ΔS, negative entropy change

entropy of the system decreases

Gibbs Free Energy (G)

describes the thermodynamic favorability of a certain chemical reaction

+ ΔG

Not spontaneously thermodynamically favorable (likely to occur)

-ΔG

Spontaneously thermodynamically favorable (likely to occur)

Exothermic, increase in entropy

Always favorable

Exothermic, decrease in entropy

Favorable at low temps

Endothermic, increase in entropy

Favorable at high temps

Endothermic, decrease in entropy

Never favorable

kinetic control

When a reaction is thermodynamically favorable but does not appear to make products at a measurable rate

Processes under kinetic control have a ____ activation energy

Large

Predicting entropy off of physical changes 1

The greater the disorder or randomness in a system, the larger the entropy

Predicting entropy off of physical changes 2

The entropy of a substance always increases as it changes from solid to liquid to gas.

Predicting entropy off of physical changes 3

When a pure solid or liquid dissolves in a solvent, the entropy of the substance increases (carbonates are an exception!--they interact with water and actually bring MORE order to the system)

Predicting entropy off of physical changes 4

When a gas molecule escapes from a solvent, the entropy increases

Predicting entropy off of physical changes 5

Entropy generally increases with increasing molecular complexity (crystal structure: KCl vs CaCl2) since there are more MOVING electrons!

Predicting entropy off of physical change 6

Reactions increasing the number of moles of particles often increase entropy.(only for g and aq)