Untitled - Kelly Walsh High School

Entropy and Free Energy 259
Be Careful!
At its melting point the heat of fusion for aluminum is 10.04 kJ/mol, and the
entropy of fusion is 9.50 J/molK. Estimate the melting point of aluminum.
The freezing point (or the melting point) is an equilibrium process. For any
equilibrium process, ∆G is equal to 0. We can add this information to the following
equation:
∆G 0 ∆H T∆S
This equation rearranges to:
T
We can enter the values given in the problem, and a kJ/J conversion to find the
temperature.
T 1056.8 K 1.06 103 K
The value of Kp for the following equilibrium at 298 K is 4.17 1014 (10.04 kJ/mol) (10
(9.50 J/mol·K)
. Calculate
the value of ∆G°, at this temperature for the equilibrium:
3 H
J)
S
(1 kJ)
2 O 3(g) K 3 O 2(g)
The following equation relates the Gibbs free energy to an equilibrium constant:
∆G RT ln K
H
S
We can enter the appropriate values into this equation to get the result:
∆G (298 K) ln (4.17 1014 )
8.314 J
∆G a (298 K)(33.6641)
mol·K b
8.314 J
a
mol·K b
∆G 83405.23 8.34 10 4 J/mol
Some instructors may wish you to report this value as kJ/mol instead of J/mol.