Question

The enthalpy of fusion for Lauric acid (C12H24O2) is 32.86 kJ/mol and enthalpy of vaporization is 63.82 kJ/mol. The melting point is 43.2 degrees C. How much heat is absorbed to raise the temperature of a 0.650g sample from 22.0 degrees C to 56.3 degrees C? The heat capacity of the solid is 2.15 J/g degrees C and the heat capacity of the liquid is 3.62 J/g degrees C

Answer 1

Reaching melting point

The heat capacity of the solid is 2.15 J/g degrees C

The soild temperature must be raised 43.2 degrees to reach melting point

(43.2-22) x 0.650 x 2.15 = 12.455 J

Melting solid

The enthalpy of fusion is 32.86 x 10³J/mol

0.650 x 32.86 x 10³ = 21.359 x 10³

Heating Solid

heat capacity of the liquid is 3.62 J/g degrees C

(56.3-43.2) x 0.650 x 3.62 = 45.35 J

Total

The total heat required to change .65 g solid to reach 56.3:

12.455 + 21.359 x 10³ +45.35 J = 21416 J or 21.416 kJ