INTRODUCTION TO GEOCHEMISTRY (GCH 3303) HOMEWORK #8 Due: April 10h, 2018 This ho

Question

INTRODUCTION TO GEOCHEMISTRY (GCH 3303) HOMEWORK #8 Due: April 10h, 2018 This homework is due at the start of class. If you wish to use your homework for studying for the mid-semester exam, then make a copy of it before turning it in. The material covered in this homework assignment relates directly to thermodynamics. Show all your work 1. Write an equation for the reaction of annite (KFesAlSisO o(OH)2) and pyrope garnet MgAbSi O2) to form phlogopite (KMgAlSisOo(OH)2) and almandine ganet (FesAl Si O12). 2. Is the enthalpy of the above reaction exothermic or endothermic at 25 °C? 3. Calculate the change in volume for the reaction at standard conditions. 4. Which of the two mineral pairs would you expect to be stable at high pressure? Why? 5. Determine which of the two mineral pairs has the greatest entropy at 25 C. 6. Determine which of the two mineral pairs has the greatest entropy at 500 oC. 7. Which of the two mineral pairs is most stable at 25 C and 1 bar? Show by calculation. 8. Calculate the equilibrium constant for the reaction at standard conditions. 9. Use the Clapeyron Equation to calculate the slope of the phase boundary between the products and reactants. Make sure that slope is in units of bar K- 10. Using the calculated data, sketch and annotate a pressure-temperature phase diagram of the reaction. Thermodynamic Data AH(J mol) P mol K (cm mol Mineral Formula -5167.24 -6284.62 KMgA?S?,010(OH)2-6392.88 -5261.3 354.9 260.76 Annite Pyrope garnet MgAl Si,012 Phlogopite Almandine garnet FeAl Si,02 154.4 113.270 149.91 115.11 342.6 Molar heat capacities in J K are -513.4479 -0.0560125 2108.739 7150315 -3.081 x 10

Explanation / Answer

KFe3AlSi3O10(OH)2 + Mg3Al2Si3 O12 < > KMg3AlSi3 O10 (OH)2+ Fe3 Al2 Si3 O12

This is equation for reaction between Annete and pyrope garnet. The sign <> is for arrow leads to forward reaction only.

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