Spontaneity of Solid Phase Change?

Question

Two crystalline forms of white phosphorus are known. Both forms contain P4 molecules, but the molecules are packed together in different ways. The alpha form is always obtained when the liquid freezes. However, below -76.9 °C, the alpha form spontaneously converts to the beta form.

P4(s, alpha) -> P4(s, beta)


Indicate which of the following statements are true or false, with regard to the above process.


a. Below -76.9°C, the sign of ΔG for this process is negative.
b. The alpha phase has the more ordered crystalline structure.
c. At -76.9°C, the two solid phases cannot coexist.
d. The sign of ΔH for this process is negative.
e. At -76.9°C, ΔG for this process is less than zero.
f. The sign of ΔS for this process is positive.

Answer 1

b. False (beta is, form at lower temp)
c. False (equilibrium point)
d. True (deltaS is neg, TdelS is neg, so delH is -
(delG=0 at equ and -TdelS is +)
f. False (see above)
e. False (see above)