- #1
cheme2019
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Homework Statement
Calcium carbonate primarily occurs as two crystalline forms, calcite and aragonite. The value of∆!° for the transition
CaCO3(calcite) ⇌ CaCO3(aragonite)
is +1.04 kJ·mol-1 at 25°C. At that temperature the density for calcite is 2.710 g·cm-3, and that of aragonite is 2.930 g·cm-3. At what pressure will the two crystalline phases be at equilibrium at 25°C?
Homework Equations
ln(ai)= ((molar V)/RT) * (P-1)
ΔG = -RT * ln(Kp
Kp = aaragonite/acalcite
The Attempt at a Solution
So I started by finding the molar volume of each by dividing the MW by the individual density and got
Vara = 34.157 cm^3/mol and
Vcal = 36.930 cm^3/ mol
From here I used the activity equation to get that
ai = e^(((molar V)/RT) * (P-1)))
And since
Kp = aaragonite/acalcite and
ΔG = -RT * ln(Kp
I can write that
ΔG = -RT * ln(aaragonite/acalcite)
This leads to
ΔG = -RT * (((molar Vara/RT) * (P-1) - ((molar Vcal/RT)*(P-1))
Or
ΔG = - molar Vara*(P-1)+(molar Vcal*(P-1))
Continuing
1040 J/mol =(-34.157 cm^3/mol ) * P + 34.157 cm^3/mol +(36.930 cm^3/mol) * P - 39.630 cm^3/mol
Solving for P I get 376 J/cm^3.
I am given that the answer is 3850.9 but no units and I wasn't able to convert my units to get that number...
I'm pretty sure my math is correct but I think I messed up on units somewhere. Any help would be greatly appreciated! Thanks!