Chemical Equilibrium Misconceptions
This material is replicated on a number of sites as part of the SERC Pedagogic Service Project
In this geochemistry activity, students explore a STELLA model of anhydrite-solution equilibrium. They find ways to illustrate several points about chemical equilibrium that address common misconceptions using this model. Then they write a mock research paper about addressing common misconceptions about chemical equilibrium in the classroom.
- Equilibrium is the state where the rates of the forward and reverse reactions are equal, not when the rates reach zero. (Common misconception: Nothing is happening at equilibrium.)
- The equilibrium constant is equal to the rate constant of the forward reaction divided by that of the reverse reaction.
- Equilibrium constants can change with temperature when the activation energies of forward and reverse reactions are different. (Common misconception: Equilibrium constants are constant under all conditions.)
- Le Chatelier's Rule. (Common misconception: Students sometimes have a hard time getting the idea that Le Chatelier's Rule is about perturbing an equilibrium state, driving the system to a new equilibrium state.)
- It doesn't matter how much of a solid is present when it is at equilibrium with a surrounding solution. The concentrations of the aqueous species will still end up being the same. (Common misconception: Students usually think that if you add more solid, the equilibrium concentrations of the aqueous species will go up. This is a misapplication of Le Chatelier's Rule.)
Context for Use
Description and Teaching Materials
In this activity, I first give the students a quick survey to assess whether they can correctly answer some questions about chemical equilibrium that target specific misconceptions. Then they do an activity where they explore a STELLA model that illustrates several concepts about equilibrium related to these misconceptions. They then take the same survey again and use the "data" from the survey to write a J. Geosci. Ed. paper about how you can use a STELLA model to address student misconceptions about chemical equilibrium. I confer with the students about their rough drafts to make sure they are explaining both the proper conceptions and the common misconceptions correctly. All this might seem like overkill, but in my experience this is what it takes to beat out some of the misconceptions students just can't seem to lose.
Teaching Notes and Tips
The Organizing Scientific Writing activity may aid students in developing their scientific writing skills.