Questions from class - Lecture 7

Question 1

Which important parameter appears in the enthalpy of mixing and how does it depend on temperature?

Answer 1

The Flory-Huggins interaction parameter. It goes as 1/T, but will depend on the energy balance of the interactions between species A and B. When the balance is negative, the interaction parameter will increase as the temperature increases - when the balance is positive, the interaction parameter will decrease as the temperature increases.

Question 2

How is the stability of a mixture evaluated on the basis of the shape of the curve describing the free energy of mixing?

Answer 2

When the second derivative of the free energy of mixing is greater than 0, it is stable, and when it is less than 0, it is unstable.

Question 3

How is the phase diagram of a mixture derived from the energy of mixing?

Answer 3

Calculate free energy from many temperatures, and plot the binodal and spinodal curves from the minima and inflection points respectively.

Question 4

Where is the critical point?

Answer 4

The critical point is the lowest point on the spinodal curve.