Exercises in the Geochemical Kinetics of Mineral-Water Reactions: The Rate Law and Rate Determining Step in the Dissolution of Halite

Michael A. Velbel
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Michigan State University
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Summary

This module consists of a laboratory exercise and related homework problems on geochemical kinetics of mineral-solution reactions for undergraduate mineralogy. Students measure the grain sizes of equant halite crystals, and the time for complete dissolution of each grain. From these data, students retrieve a rate law, from several possible. Additional homework problems allow various chemical and physical transport processes in mineral-fluid systems to be evaluated.

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Context

Audience

This activity is designed for an undergraduate required course in mineralogy and is generally for sophomore or junior level students.

Skills and concepts that students must have mastered

A treatment of chemical kinetics (rate laws, diffusion) equivalent to that of chapter 3 in Gill (1995) is assumed. I also require the students to read Berner (1978), for its emphasis on low-temperature aqueous reactions. Treatments comparable to either or both of these references are found in Brownlow (1996, p. 210-213 and p. 355-365), Krauskopf and Bird (1995, ch. 11), Drever (1988, ch. 7; 1997, ch. 11), Langmuir (1997, ch. 2), Faure (1991, ch. 19), and Henderson (1982, ch. 8). The treatments in Berner (1980, p. 78-79; 1981, ch. 3), Sposito (1994, secs. 1.3-1.5, 3.1 & 4.5), Lasaga (1981, ch. 1), Richardson and McSween (1989, chs. 5 & 10), Stumm (1992, chs. 5 & 6), Stumm and Morgan (1996, ch. 2 p. 58-87 & ch. 13), Nahon (1991, ch. 1) and Lerman (1979, chs. 3 & 5) are more advanced. Cussler (1984) is a superb treatment of diffusion.

The treatment of kinetics in Gill (1995), Krauskopf and Bird (1995), Henderson (1982), and Richardson and McSween (1989) emphasize applications to igneous and metamorphic rocks; the other references emphasize weathering, diagenesis, and aqueous geochemical applications. These textbooks and journal articles, and other resources useful for or cited in the homework exercises, are included in the reference list.

How the activity is situated in the course

This activity is a stand-alone exercise, but is part of a larger volume of classroom and laboratory activities from "Teaching Mineralogy," a workbook published by the Mineralogical Society of America, Brady, J., Mogk, D. W., and Perkins, D., (editors), 1997,406 pp.

Goals

Content/concepts goals for this activity

The lab and homework illustrate several basic principles of chemical kinetics directly relevant to geology, including rate laws of reactions, diffusion, advective transport, and the relationship between rate-limiting mechanisms and crystal-surface morphology.

Higher order thinking skills goals for this activity

This activity involves data analysis and synthesis of ideas.

Other skills goals for this activity

This activity involves writing, operating analytical equipment, and working in groups.

Description of the activity/assignment

This module consists of a laboratory exercise and related homework problems on geochemical kinetics of mineral-solution reactions for undergraduate mineralogy. Students measure the grain sizes of equant halite crystals, and the time for complete dissolution of each grain. From these data, students retrieve a rate law, from several possible. Additional homework problems allow various chemical and physical transport processes in mineral-fluid systems to be evaluated.

The lab and homework illustrate several basic principles of chemical kinetics directly relevant to geology, including rate laws of reactions, diffusion, advective transport, and the relationship between rate-limiting mechanisms and crystal-surface morphology.

Determining whether students have met the goals

Students have met the goals of this activity if they thoroughly and correctly answer the homework questions provided within the activity download (see below).

More information about assessment tools and techniques.

Teaching materials and tips

Other Materials

Supporting references/URLs

Brady, J., Mogk, D. W., and Perkins, D., (editors), 1997, Teaching Mineralogy, a workbook published by the Mineralogical Society of America, 406 pp.

Mineralogical Society of America - Join today!

A more comprehensive list of references is listed in the activity (see file downloads above).

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