Department of Earth Science |Northeastern Illinois University

AQUEOUS GEOCHEMISTRY
ESCI 406
Spring, 2005
Homework #3: Due Wednesday, March 3, 2005                                                                     Sanders

Complete and hand in both parts of this homework assignment.

PART I:  Problems from the end of Chapter 2 of the Eby textbook.

        # 23 (a, b, and c)
        # 24(a); also answer the question from part b:  "What is the solubility of magnesite in pure water?"  In other words, how much (what mass of) magnesite will dissolve in a given volume of pure water?
        # 28 (a, b)  Please note: the data tabulated in this problem are for the reactions involving the organic liquid " the organic liquid dissolved in water.  So, for example, for the reaction TCE " TCE dissolved in water, the DG_R is +11.282 kJ/mol.

PART II: Portfolio of Analyses

* The objective of this assignment is to propose a geochemically relevant reaction for each of the five analysis sets that you have collected, and to determine the equilbrium constant for each reaction.  This homework assignment will form the first entry in your Portfolio of Analyses.  Please hand it in with the whole portfolio.  I will look at and potentially comment on the whole portfolio, but only this week's assignment will be graded.

The Assignment For each of your analysis sets, examine the data and the associated journal article (if any).  Come up with a geochemical reaction that is relevant to that particular setting.  (For example, if your analysis set contains samples of stream water from the Canadian Shield, you might consider a feldspar weathering reaction to be particularly relevant.  If your analysis set contains samples of ground water from a karst region in Kentucky, you might consider a calcite dissolution reaction as particularly relevant.)  For many journal articles, the article itself will suggest several reactions that might be of interest. Write and balance a chemical equation for the reaction you chose.  Use a different one for each of the analysis sets.  CAUTION:   Eventually we are going to look at concentrations of various dissolved materials in the water and determine if the waters are in equilibrium with respect to this reaction.  So be sure to choose an equation that involves dissolved species for which you have chemical analytical data!  Explain in a paragraph for each analysis set why the reaction you chose was geologically relevant to the particular setting. Next, using thermodynamic data from your textbook or from any of the many sources available online or in books on the cart, calculate the equilbirium constant for the reaction you have developed. Do this for each of the five analysis sets.  You should end up with chemical equations for five different chemical reactions (one for each analysis set), as well as DGRo values and Keq values for each one. What to Put in the Portfolio * State the objective and explain what the term equilbrium constant means and how it relates to the thermodynamic data (DGRo and DGR) one uses to calculate it * Describe your methods * Summarize your results in a neat table. * Discuss your results (e.g compare and contrast, put the results in their geologic context, etc.)

* Create a cover page for this section called "Equilibrium Constants for Geochemical Reactions". 

* Cite the source of every piece of information that is not taken from your own brain.  Use standard citation format!  (e.g. "Eby, 2005")

* Check your "References Cited" page, and make sure it includes all of the sources you have cited thus far, in proper format. 

* Hand in the whole portfolio with all the components listed here:
    - cover page
    - the section on Equilibrium Constants for Geochemical Reactions (the current assignment)
    - cover page for each analysis set
    - five analysis sets
    - References Cited

* Use dividers, tabs, or colored pages between sections.

© 2005 Laura L. Sanders.  Last updated February 23, 2005.