Thermodynamics + Spontaneity

Spontaneous

process will occur under given conditions, irreversible, releases energy

Reversible Process

can only occur at equilibrium, no free energy

ΔH

enthalpy

Exothermic- favorable

Endothermic- unfavorable

ΔS

entropy “dissorder”

favorable if positive

1st Law of Thermodynamics

energy can’t be created or destroyed

2nd Law of Thermodynamics

sum of all entropy in the universe is always increasing

3rd Law of Thermodynamics

a perfect crystal at 0 K has an absolute entropy at 0 J/mol K

Finding ΔS, ΔH, and ΔG

Δ=(sum of products x coef.)-(sum of reactants x coef.)

States Conditions

G>L>S

largest to smallest ΔS

Molar Mass Conditions

larger molar mass is larger ΔS

Allotropes

less concentrated structure is larger ΔS

(graphite and diamond)

Molecular Complexity

more complex larger ΔS

Dissolution

dissolved solution is larger ΔS

Temperature

higher temp is larger ΔS

exothermic → heat added to surroundings → increase entropy in surrounding

ΔSuniverse

ΔSuniverse = ΔSsys + ΔSsurr

ΔSuniv>0 = spontaneous

ΔSuniv<0 = reversible

ΔSsurr

ΔSurr=-qsys/Tsurr=ΔHsys/Tsurr

Gibbs Free Energy (ΔG)

max amount of energy released from a system that is available to do work

theoretical number

NEGATIVE WHEN SPONTANEOUS

ΔG=ΔHsurr-TsurrΔsys

Reversible Reactions

if achieves theoretical limit

ΔG=ΔG+RTlnQ

or at equilibrium (ΔG=0) ΔG=-RTlnK

Q>K

reverse spontaneous reaction

Q<K

forward spontaneous reaction

Q=K

equilibrium (ΔG=0)

kJ → J

kJ x 1000 = J