During chemical weathering, forsterite is dissolved by thecarbonic acid in rainwater. The weathering reaction is:
Mg2SiO4 forsterite + 4H2CO3 (aq) ? 2Mg2+ + 4HCO3- + H4SiO4 (aq)Use the thermodynamic data from Appendix II, source 2, for thefollowing calculations.
4a. Calculate the Keq for this weathering reaction at 25 �C.
4b. If the reaction is at equilibrium, using Le Cha?telier�sprinciple, predict what would happen if Mg2+ ions were added to thesolution
4c. Using Le Cha?telier�s principle, predict what would happento the equilibrium constant if the reaction occurred at a highertemperature.
4d. Calculate the Keq for this reaction at 40 �C. Does thesolubility of forsterite increase or decrease with increasingtemperature? How does this result compare with your prediction inpart (c).
Appendix II standard state = 298.15 k 10^5 pa
Mg2SiO4 =
Delta G f= 2056.7 kJ mol^-1
Delta H f= 2175.7 kJ mil ^-1
S= 95.2 J mol^-1 k^-1
4H2CO3 =
Delta G f= 623.14 kJ mol^-1
Delta H f= 699.09 kJ mil ^-1
S= 189.31 J mol^-1 k^-1
2mg^2+ =
Delta G f= 455.4 kJ mol^-1
Delta H f= 467.0 kJ mil ^-1
S= 137 J mol^-1 k^-1
4HcO3^- =
Delta G f= 586.8 kJ mol^-1
Delta H f= 689.93 kJ mil ^-1
S= 98.4 J mol^-1 k^-1
H4SiO4 =
Delta G f= 1307.9 kJ mol^-1
Delta H f= 1457.3 kJ mil ^-1
S= 180 J mol^-1 k^-1
