1.4 Free Energy

What is the Gibbs Free Energy equation?

∆𝐺 = ∆𝐻 − 𝑇∆S

How do you determine spontaneity using ΔG?

• ΔG < 0 → Spontaneous

• ΔG > 0 → Nonspontaneous

• ΔG = 0 → Equilibrium

When using ΔG = ΔH − TΔS, what unit conversion is required?

Convert ΔS from J to kJ by dividing by 1000 before calculating ΔG.

How do you calculate ΔG° from standard enthalpy and entropy?

• Calculate ΔH°

• Calculate ΔS°

• Convert ΔS° from J → kJ

• Plug into

How do you calculate ΔG° for coupled reactions?

• Add the reactions together.

• Cancel any species that appear on both sides.

• Add the ΔG° values.

ΔH and ΔS are BOTH positive.

When is the process spontaneous?

High temperature

ΔH and ΔS are BOTH negative.

Low temperature

ΔH is positive and ΔS is negative.

Never

ΔH is negative and ΔS is positive.

When is the process spontaneous?

Always