During chemical weathering, forsterite is dissolved by the carbonic acid in rainwater. The weathering reaction is: Mg2SiO4...

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Chemistry

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

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4.3 Ratings (872 Votes)
Mg2SiO4 forsterite 4H2CO3 aq 2Mg2 4HCO3 H4SiO4 aq 4a Calculate the Keq for this weathering reaction at 25 C For KEq we need dG dG RTlnK K expdGRT dG Gproducts Greactants 24554 4586813079 20567462314 1664 kJmol 16640 Jmol then K exp16640 8314298 8257 4b    See Answer
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