1.8.2 Gibbs free energy, entropy change

ΔS - entropy change, J K^-1 mol^-1

S is a measure of disorder / the energy of the system

increased ΔS = increased disorder

disorder increased for gases
disorder increased if number of moles increases
disorder increased if temperature increases, as particles gain (kinetic) energy and move further apart

at 0 Kelvin, crystal is perfectly ordered, so entropy is 0 J K^-1 mol^-1

ΔS = ΣS_products - ΣS_reactants

Gibbs free energy change, kJ mol^-1

ΔG = ΔH - TΔS

feasible = a reaction that is energetically possible and likely to occur spontaneously

feasible reactions go spontaneously in the direction of increasing disorder, so have a positive ΔS
ΔG ≤ 0 for a feasible reaction
- ΔG = ΔH - TΔS
- ΔG more likely to be negative if ΔH is negative and ΔS is positive
changing temperature or reaction type changes feasibility

at the melting point

there’s a sudden increase in S
- molecules lose their fixed arrangement and absorb heat energy
- increased kinetic energy, increased disorder
ΔG = 0
- the solid and liquid states coexist
- the rate of melting = the rate of freezing

ΔS of vaporisation > ΔS of fusion, because a gas is more disordered than a liquid or solid