TWQ Exercise

Dexter Perkins
University of North Dakota
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This is an exercise using TWQ to generate a phase diagram. It can be used as homework but is better done in a group.

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I use this in my junior level petrology class.

Skills and concepts that students must have mastered

Before doing this, the students have already become familiar with phase diagrams and with the basics of thermodynamics. The have calculated and plotted a few simple reactions, starting with thermodynamic data. They have also worked with the phase rule.

How the activity is situated in the course

My class is all project based. This is but one of many. It is done by groups of students. We start it during normal class time but they never finish -- they get together at other times to complete it. This is sufficiently challenging for some students -- so, I have to be available.


Content/concepts goals for this activity

This expands students' understanding of phase diagrams, the phase rule, and thermodynamics. After they complete this they should be able to interpret complex phase diagrams and to explain how they can be calculated and plotted. They will also be able to say why computers are absolutely essential for such calculations.

Higher order thinking skills goals for this activity

In some ways this is a cookbook exercise. But, the questions that are asked (see exercise handout) will push students to interpret results. Additionally, the first few questions make them apply the phase rule in a way that they have not done previously. Those that really understand the phase rule will do well. Others will not. (Most of my students fall into the second category, but not all.)

Other skills goals for this activity

It is most helpful if one person in each group has good computer skills and does not get intimidated by complex programs, messing with files, etc. One goal of this project is to help the other, less experienced computer users, to hone their skills.

Description of the activity/assignment

This activity is a problem set/project that involves applying the phase rule to a model chemical system, and then calculating a phase diagram for that system using TWQ. Students also interpret the resulting diagram -- discussing which minerals and assemblages are stable under which conditions and figuring out why.

Determining whether students have met the goals

There are, of course, correct answers to some of the questions. But, more significant -- and more difficult to determine is whether students really understand what they are doing. I evaluate this by giving them similar problems on quizzes, and also by asking them to interpret phase diagrams when they take exams.

More information about assessment tools and techniques.

Teaching materials and tips

Other Materials

Supporting references/URLs

A good and diverse collection of supporting material can be found at There are specific links on that site to pages that describe the phase rule and TWQ.

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