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Chemistry Forums for Students => Physical Chemistry Forum => Topic started by: Strike on February 02, 2012, 02:28:04 AM

Title: Finding Free Energy in Freezing water at 8.6C
Post by: Strike on February 02, 2012, 02:28:04 AM

I'm stuck on one of my practice problems in trying to freeze 94 moles of water at 1 atm and the constant temperature of 8.6 C.

The given information:

delta H_fusion = 6025 J/mol
C_{p (ice)} = 37.7 J/K mol (Heat capacities at constant pressure for ice and water)
C_{p (water, liquid)} = 75.3 J/K mol
n = 94
T = 8.6 C or 281.75 K

I got dG = dH - TdS (d = delta) and dS = dq_rev / T. My notes show these formulas:

(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fi.imgur.com%2F37aKP.png&hash=60ee4f3d21775409dfa92bcf8ada6d6fb13a0da9)

(Apparently at constant pressure, the q is equal to dH during phase change - fusion in this case..)

But no where does the question say this is reversible. Do I still use dH(fusion) and T to find dS and simply plug into the Gibbs formula? I also still don't have dH nor did I even touch the heat capacities.