thermodynamics, entropy, and chemical spontaneity

which phase produces the highest level of entropy?

gases

which phases produce moderate levels of entropy?

liquids and aqueous solutions

which phase produces the lowest level of entropy?

solids

when change in enthalpy (H) is positive …

the reaction is endothermic.

when change in enthalpy (H) is negative …

the reaction is exothermic (favorable).

when change in entropy (S) is positive …

disorder increases (favorable).

when change in entropy (S) is negative …

disorder decreases.

when change in gibbs free energy (G) is positive …

the reaction is nonspontaneous.

when change in gibbs free energy (G) is negative …

the reaction is spontaneous.

formula for changes in gibbs free energy (GFE)

deltaG (kJ) = deltaH (kJ) - temp (K) x deltaS (J/K)

the sign of changeG when changeH ( - ) and changeS ( + ) is …

negative (spontaneous at all temps)

the sign of changeG when changeH ( + ) and changeS ( - ) is …

positive (nonspontaneous at all temps)

the sign of changeG when both changeH and changeS ( + ) is …

temperature dependent; negative/spontaneous at high temps, positive/nonspontaneous at low temps

the sign of changeG when both changeH and changeS ( - ) is …

temperature dependent; positive/spontaneous at high temps, negative/nonspontaneous at low temps

what is changeS determined by?

the change in gas amount throughout chemical reactions.

if there's more reactant gas …

entropy decreases.

if there's more product gas …

entropy increases.

what is the given temperature?

298 K

formula for temp when changeG = 0

T(changeG = 0) = changeH/changeS

rule of thumb for significant figures?

round to 3 sig figs (2 to 4 if absolutely necessary)

before finding deltaG …

make sure all joule units are the same (1000 J = 1 kJ)