Question

Consider plastic bottles that are made for filling juice. The melting point of the material is 41°C. Also, we get the ΔHm= 9kcal/mol through melting experiment.

a. Calculate the entropy change of melting ΔSm

b. Calculate the free energy change of melting ΔGm

c. Will the bottle become more or less ordered after melting? Why?

Answer 1

a) S = H/T

H = 9000 cal/mol

T = 41 C = 41 +273 = 314 K

S = 9000 cal/mol / 314 K = 28.6624 cal/mol K

b) Change in free energy is given by,

G = H - TS

G = 9000 - (28.6624*314) = 0

This means that the system is at equilibrium.

c) As S is positive there is an increase in entropy.and thus the molecules inside the bottle will become more disordered. In solid state , the molecules are fixed at one position, but as heat is supplied, this energy is transferred to molecules which start colliding and moving , i.e their mobility increases. This results in disordering of the system.