|Water transfer equilibrium analogy.|
The first thing I did was show the students the "Red Pill or Blue Pill" clip from the Matrix. I likened equilibrium with taking the red pill because you have to open your eyes to the real world of chemistry. We can no longer pretend that every reaction goes all the way to completion! Maybe this scared the kids more than amused them, but I found it very funny.
|Using two different sizes of straws to transfer water.|
Now the students were ready to put some numbers to their water transfer equilibrium analogy. The students conducted the classic experiment with two graduated cylinders and two different sized straws. They used the straws to transfer water from one graduated cylinder to the other, each time measuring the volume in the two cylinders. (By the way, McDonalds has really large straws that are perfect for this activity.) The result is a beautiful graph of the concentration of the "reactants" and "products" as they approach equilibrium. It only took about six transfers for the system to reach equilibrium, which was just about all the patience my students had for the water transfer with drinking straws. I loved how the volume in each graduated cylinder was different at equilibrium, even though the amount of water transferred was the same.
|Checking the volumes at equilibrium.|
|Penny transfer equilibrium activity.|
On Day Two of our equilibrium unit, I split the kids into groups of three or four and gave them a POGIL to work through. The POGIL activity inched them a little closer toward the equilibrium expression because the examples were based on a chemical reaction ( A <-> B). This activity is also data driven, similar to the penny and the straw water transfer, but using moles of A and B. Each student was given a different set of starting conditions for one of two equilibrium systems. By sharing their results, the class derived the results necessary to calculate the ratio of products to reactants. The POGIL was the perfect transition from the reversible reaction concept to an equilibrium expression calculation using molarity, and determining the increase and decrease of the species in the system.
|The class agenda for Day Three of the equilibrium unit.|
On Day Three I taught the kids how to write an equilibrium expression and use it for calculations. I was so pleased at how quickly they mastered this new skill. I believe that the two days of hands-on activities and equilibrium analogies gave them the perfect conceptual groundwork for understanding the equilibrium expression.
|Adding stress to the system by inhibiting the decomposition reaction.|
Tomorrow we will head into the lab for the AP Chemistry lab kit exploring Le Chatelier's Principle using real chemical reactions.
Note: these activities are all available on the Flinn e-learnig video library.