Tutorial Exploring the Impact of Initial Moles of Reactants on Reactant Progress

Terri Woods, East Carolina University (retired)

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When studying the Law of Mass Action, students usually understand how increasing temperatures can increase the rate of a reaction but often can't visualize the impact of increases in the mass of reactants. This mathematically straightforward exercise allows them to calculate the change in moles of products due to an increase in moles of reactants.

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graduate and upper level undergraduate course in low-temperature geochemistry

Skills and concepts that students must have mastered

Writing equilibrium constants
Use of ICE tables from basic chemistry

How the activity is situated in the course

This classroom activity is pursued soon after introducing the Law of Mass Action and the concept of equilibrium constants.


Content/concepts goals for this activity

Writing expressions for equilibrium constants of chemical reactions

Using amounts of reactants and products provided to calculate values for equilibrium constants

Employing basic algebra to determine the concentrations of reactants and products at equilibrium using initial concentrations of reactants and reaction stoichiometry.

Higher order thinking skills goals for this activity

Studying simulated results of chemical reactions and drawing conclusions about how initial moles of reactants influence reaction progress

Other skills goals for this activity

Description and Teaching Materials

This activity closely follows the presentation by Jack E. Fernandez in his book entitled, Modern Chemical Science (pp.173-176; The Macmillan Company, 1971). It is an interactive classroom presentation created in Powerpoint that walks students step-by-step through the process of evaluating how changes in initial moles of gaseous reactants influences how far a reaction proceeds.
Tutorial_Investigation of Impact of Concentration of Reactants on Reaction Progress (PowerPoint 2007 (.pptx) 91kB Nov1 21)

Teaching Notes and Tips

I suggest going through the tutorial in class with the students allowing them to complete each step before clicking to show the correct answer to them on the screen. I also provide this tutorial to them so they can refer to it when they are doing exercises for their problem sets.


As we progress through the tutorial in class, I regularly check with students to ensure they understand where the answers are coming from and feel comfortable that they could repeat these steps on their own with additional examples.