The shells of marine organisms contain calcium carbonate CaCO3, largely in a crystalline form known as calcite. There is a second crystalline form of calcium carbonate known as aragonite. Physical and thermodynamic properties of calcite and aragonite are given below.

Properties
(T=298K, P=1atm) Calcite Aragonite
ΔH°f (kJ/mole) -1206.87 -1207.04
ΔG°f (kJ/mole) -1128.76 -1127.71
S° (J/mole K) 92.88 88.70
C°P (J/mole K) 81.88 81.25
Density (gm/mL) 2.710 2.930
A) Based on the thermodynamic data given, would you expect an isolated sample of
calcite at T=298K and P=1 atm to convert to aragonite, given sufficient time.
Explain.

B) What pressure must be achieved to induce the conversion of calcite to aragonite at
T=298K. Assume both calcite and aragonite are incompressible at T=298K.

C) Suppose the pressure is P=1.00 atm and the temperature is increased from
T=298K to T=400K. Based on this calculation, can isolated calcite be converted
to aragonite at P=1 atm if the temperature is increased? Explain.

D) Suppose the pressure is increased from P=1.00 atm to P=1000 atm and the
temperature is increased from T=298K to T=400K. Which form of CaCO3 is more
stable under these conditions?

Expert Answer