Question

(40 pts) Chapter 3, problem 15. The shells of marine organisms contain CaCO3, largely in the crystalline form known as calcite. There is a second crystalline form of CaCO3 known as aragonite.

a. Based on the thermodynamic and physical properties given for these two crystalline forms, would you expect calcite in nature to convert spontaneously to aragonite give sufficient time? Justify your answer.

b. Will the conversion proposed in part (a) be favored or opposed by increasing the pressure? Explain. c. What pressure should be just sufficient to make this conversion spontaneous at 25oC?

d. Will increasing the temperature favor the conversion? Explain. (Note from SRB: In this table, the subscript “m” indicates that this variable is per mole, similar to the overbar that we have been using in the lectures).

Properties at 298 K	(calcite)	(aragonite)
ΔfHo m (kJ/mol)	-1206.87	-1207.04
ΔfGo m (kJ/mol)	-1128.79	-1127.71
So m (J/mol K)	92.88	88.70
Cp,m (J/mol K)	81.88	81.25
Density (g/cm3 )	2.710	2.930

Answer 1