# Problem: As O2 (l) is cooled at 1 atm, it freezes at 54.5 K to form Solid I. At a lower temperature, Solid I rearranges to Solid II, which has a different crystal structure. Thermal measurements show that ΔH for the I→II phase transition = -743.1 J/mol, and ΔS for the same transition = -17.0 J/K mol. At what temperature are Solids I and II in equilibrium? A. 2.06 K B. 43.7 K C. 31.5 K D. 53.4 K E. They can never be in equilibrium because they are both solids.

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###### Problem Details

As O2 (l) is cooled at 1 atm, it freezes at 54.5 K to form Solid I. At a lower temperature, Solid I rearranges to Solid II, which has a different crystal structure. Thermal measurements show that ΔH for the I→II phase transition = -743.1 J/mol, and ΔS for the same transition = -17.0 J/K mol. At what temperature are Solids I and II in equilibrium?

A. 2.06 K

B. 43.7 K

C. 31.5 K

D. 53.4 K

E. They can never be in equilibrium because they are both solids.

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