Chem 111 for January 29

It's the end of January and time for me to proclaim the importance of the balanced equation. They're really, really important. I really like balanced equations. Everything we do in this part of Chem 111 comes back to the balanced equation as the fundamental summary of a chemical reaction. As Neil says, "It's all one song."

We started by establishing a general process for calculating the amount of product from a given amount of reactant. While that assumes that other reactants are in excess, I didn't want to dwell on that just yet. We keep stressing that the importance of the balanced equations is that it gives you the molar ratios. Being able to write those consistently and completely (I like putting the verbs in: 2 moles CO₂ produced/2 moles O₂ consumed), understanding what they mean and knowing how they're applied, is the best thing students can do in their understanding of stoichiometry.

From there, it was on to limiting reactants. I've cast the Moog-Farrell limiting reagent activity from S'Mores into atoms and molecules, with--I think--positive results. I used all the same ratios and many of the same words, and since the students this semester appear to be much more comfortable with atoms, molecules and moles, they were able to get the concept very quickly.

With one big exception. Many students stated that the reactant with the smallest amount was the limiting reactant even when they had already done an example where that was not the case. So it's back to those molar ratios--can they consistently and reliably apply them?

But what they are getting is that the limiting reactant runs out first and the reaction stops as soon as that happens. That's something to build on.

Tomorrow: More balancing equations, more limiting reactants, and Quiz 2.