Using the following data: C2F2(g), deltaG0f (kJ/mole)= 191.2, deltaH0f (kJ/mole)

Question

Using the following data:

C2F2(g), deltaG0f (kJ/mole)= 191.2, deltaH0f (kJ/mole)= 241.3

C6F6(g),deltaG0f (kJ/mole)= 78.2,deltaH0f (kJ/mole)= 132.8

Calculate deltaS0 at 298K, Keq at 298K, and estimate Keq at 3000K, assuming the deltaH0 and deltaS0 are independent of temperature.

d at 1 atm, it freezes at 54.5K to form I. At a lower temperature, solid I rearranges to solid II, which has a different crystal structure. Thermal measurements show that deltaH for the I---->II phase transition is -743.1 J/mole, and deltaS for the same transition is -17.0 J/K/mole. At what temperature are solids I and II in equilibrium?

Explanation / Answer

G(rxn) = 3(191.2) - 78.2 = 495.4 KJ

H(rxn) = 3(241.3) - 132.8 = 591.1KJ

therefore, S = (G - H)/T = -320.6 J/K

Keq = exp(-G/RT) = 1.62e-87

Keq at 3000k = exp(-G/RT) = 2.37e-9

and

the phases are in equilibrium when delta G = 0

let the temp be T
so

G = H-TS = 0

put all values,

T = H/S = -743.1/-17 = 43.71K

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