Gibbs Free Energy and Spontaneity

Entropy method

(change in)Stotal must be used to determine entropy. (delta)Stot=(delta)S-(delta)H/T > 0 is spon (delta)Stot=0 is equilibrium (delta)Stot<0 means nonspon/reverse reaction is spon

Gibbs at different temperatures

(delta)G=(delta)H-T(delta)S H and S positive: spontaneous at high temps H and S negative: spontaneous at low temps H neg and S pos: Always spontaneous H pos and S neg: Never spontaneous

Gibbs Free energy

(delta)G=(delta)H-T(delta)S How to derive: (delta)G=-T(delta)Stot

Using Gibbs free energy to determine spontaneity

(delta)G=(delta)H-T(delta)S<0 is spon (delta)G=0 is equilibrim (delta)G>0 is nonspon opposite of (delta)Stot entropy

What is Van't Hoff Plot

Derive with relationship between entropy and enthalpy with equilibrium constant: ΔH°-TΔS°=-RTlnK lnK=-ΔH°/R(1/T)+ΔS°/R Plot: 1/T for x; vs lnK for y

Van't Hoff Plot finds

Enthalpy and entropy; m = -ΔH°/R b = ΔS°/R

Difference between Gibbs vs entropy and enthalpy

Gibbs is strongly temperature dependent while H and S are not. (delta)G=(delta)H-T(delta)S

What does Gibbs free energy measure

The max amount of energy in a system that can be used as ordered energy

Another way to find Gibbs free energy

Using free energy of formation and (delta)G =sumv(delta)Gf(prod)-sumv(delta)G(react)

Gibbs free energy under nonstandard conditions

ΔG = ΔG° + RTlnQ derive: ΔG° =ΔH°-TΔS° ΔS=ΔS°-RlnQ ΔG =ΔH-TΔS ΔG =ΔH°-T(ΔS°-RlnQ) ΔG = ΔG° + RTlnQ

Determining the Temperature of an equation at equilibrium

ΔG°=-RTlnK derive: ΔG = ΔG° + RTlnQ at equilibrium (delta)G=0 Q=K at equilibrium (delta)G(standard)=-RTlnK

Relationship between Gibbs free energy, entropy, enthalpy, and equilibrium constant

ΔG°=ΔH°-TΔS°=-RTlnK