Non-Ideal solution Flashcards
non-ideal solution
molecules don’t interact identically therefore behaviour of one molecule depend on composition of solution
arrangement of molecules
non-random - strong attraction = closer
non-ideality
frequently observed IRL and make necessary to extend thermodynamics analysis
equation for chemical potential - calculate concentration
μx = μx* + RTln[ax]
concentration/activity, ax
calculated concentration
activity coefficient - Yx equation
Yx = ax / [x]
[x]
actual concentration
ax
effective concentration
ax = [x]
ideal solution
how much Yx deviates from 1
how different solution is from ideal
effective equation - μx
μx = μx* + RTlnYx[x]
Yx converting [x] into ax
has physical significance - used to measure amount of solution deviated from ideal
ax in a graph
concentrated predicted by ideal model to have same μ as actual
if Y = 1
ideal solution
Y < 1
x is more stable than predicted model
Y > 1
x is less stable than predicted model
non-ideal +ve deviation from Raoult’s law
DH{mix} > 0 - endothermic - heat absorbed upon mixing
Total V > sum of V of components
non-ideal -ve deviation from Raoult’s law
DH{mix} < 0 - exothermic - heat evolved upon mixing
Total V < sum of V of component
ionic solution
requires knowledge of deviation for ideality
ionic solution example - NaCl in water
O2 - more electronegative than H therefore strong attraction between solvent-solvent molecule
Na+ and Cl- disrupt water bonds by hydration shell formed
has electrostatic interaction
dilute ionic solution
don’t cause non-ideal behaviour at low concentration
has affect on enthalpy and entropy when ions dissolve in water
enthalpy
ion-water electrostatic interaction is more than compensated for loss of water-water H bonds
DH = -ve
entropy
decreases as ions added to water - less disorder
water around ion - in particular arrangement
more concentrated ionic solution
significance in electrostatic interaction - charges repel and attract
DH - change in enthalpy
transferring ions from gas phase to solution
smaller ions in solution
large DH and D entropy - strong interaction with water
Debye-Huckel theory equation
calculating solute-solute electrostatic interaction in solution
log{10}Yx = -Az{x}(square root I)
finding ionic strength equation
I = 1/2 sum of c{x}Z{x}(2)