The sketch is a portion of the phase diagram for the element sulfur. The transition between solid orthorhombic (S_α) and solid monoclinic (S_β) sulfur, in the presence of sulfur vapor, is at 95.3 °C. The triple point involving monoclinic sulfur, liquid sulfur, and sulfur vapor is at 119 °C.

(a) How would you modify the phase diagram to represent the melting of orthorhombic sulfur that is sometimes observed at 113 °C? What would the phase diagram look like if the monoclinic sulfur did not form?

(b) Account for the observation that if a sample of rhombic sulfur is melted at 113 °C and then heated, the liquid sulfur freezes at 119 °C upon cooling.

Transcribed Image Text:

Pressure Sa SB Liquid Vapor Temperature