Thermodynamic - Geochemistry - Home Work, Exercises of Geochemistry

Download Thermodynamic - Geochemistry - Home Work and more Exercises Geochemistry in PDF only on Docsity! Homework 2 – Thermodynamic and Activity Calculations Aqueous Geochemistry You will need to find values for all the thermodynamic calculations from a reference for questions 2-6. Both of the references I list on the syllabus have most or all of these values. Use Excel when appropriate. 1. Write a balanced chemical reaction for the acid (H+) dissolution of anorthite (CaAl2Si2O8). The products of this reaction are the secondary mineral gibbsite (Al(OH)3) and ions in solution (Ca 2+ and H4SiO4(aq)). 2. Calculate the oRS for the reaction in Question 1 using values for o fS of the reactants and products. 3. Calculate the oRH for the reaction in Question 1 using values for o fH of the reactants and products. 4. Calculate the oRG for the reaction in Question 1 using o RH and o RS . 5. Calculate the oRG for the reaction in Question 1 from the table of values for o fG of the reactants and products. Calculate eqK of the reaction based on the new o RG . 6. Using the ofG values, calculate the eqK for the reaction (CaCO3 = calcite): CaCO3 + H +  Ca2+ + HCO3- 7. Calculate the saturation index (SI) with respect to calcite for the groundwater sample in the table below. Would you expect calcite to be actively dissolving, precipitating, or is the solution near equilibrium with calcite? Note: We are ignoring the effects of activity for this problem. Species Concentration (mg/L) Ca2+ 89.5 Mg2+ 39.4 Na+ 22.6 K+ 0.4 HCO3 - 415.0 Cl- 8.1 SO4 2- 1.9 pH 7.3 (pH units) 8. Calculate the ionic strength for the groundwater sample from Question 6. 9. Calculate the activity coefficient and the activity for all species in the groundwater sample from Question 7. Discuss your choice of activity coefficient equation. Assume a temperature of 25C. 10. Recalculate the saturation index with respect to calcite for the groundwater sample from Question 7, this time using activity instead of concentration. Docsity.com