Question

Estimate the lowering in melting point of PVF₂ (-CH₂-CF₂-) when it is mixed with PMMA that contains 0.6 mole fraction of PVF₂. PMMA does not crystallize. Given:

ΔH_u= 1.425 Kcal/mol, T_m⁰ =179.6°C. R= 1.98 cal/mol K

PMMA

Answer 1

Given:

Mol fraction of PVF2 = 0.6

           

PMMA                       

Tm= 179.6 deg C

Tm0 in K = 179.6+273.15 =452.75    K

Delta H = 1.425 kJ /mol = 1425 J / mol

Since the value of delta H is in J/mol we uses value of R in J / K mol

R = 8.314 J / Kmol

We use following formula

Delta T (lowering in melting point) = R T²*c_solute/ Delta H

Here c_solute is the mol fraction of solute.

Lets plug in the values

Delta T =[ (8.314 x 452.75²x 0.6)/1425 ] K

Delta T= 717.57

Delta T (lowering in melting point in deg C ) = 717.57 – 273.15 = 444.4 deg C.