APCHEM - unit 9

ap chemistry unit 9

entropy (S)

the dispersal of matter or energy in a sample of matter

changes in entropy (ΔS)

a measure of how dispersed the matter or energy is in a particular system

entropy increases when…

the matter becomes more dispersed (ex: solid to liquid, liquid to gas, or increase of the volume of gas)

total # moles of gaseous product > # moles of reactant

increase in entropy

dispersal of energy results in

an increase in entropy

as temp rises…

the entropy rises

distribution of kinetic energy among gas particles broaden as…

temperature rises

positive entropy (phase changes)

solid → liquid → gas (or moles of gas increase)

negative entropy (phase changes)

gas → liquid → solid (or moles of gas decrease)

entropy is calculated from…

absolute entropies of the involved species (before and after the process occurs)

entropy equation

ΔS°rxn = ΣS°products - ΣS°reactants

chemical reactions continue until…

equilibrium is reached

Gibbs Free Energy (ΔG)

describes whether a reaction is thermodynamically favorable or unfavorable

thermodynamically favorable changes proceed to equilibrium…

without external intervention

Gibbs Free Energy equation (with entropy)

ΔG° = ΔH° - TΔS°

Gibbs free energy by formation of products

ΔG°rxn = ΣΔG°f(products) - ΣΔG°f(reactants)

thermodynamically favored (G)

ΔG° < 0

thermodynamically unfavored (G)

ΔG° > 0

under kinetic control

thermodynamically favorable reactions, but don’t produce products at a measurable rate (typically have a large activation energy to account for slower rate of reaction)

thermodynamically favored (K)

the products are favored at equilibrium (K > 1)