Throughout the last ten years teaching both chemistry and Advanced Placement Chemistry I have realized that the concept of equilibrium does not receive enough attention in my first-year chemistry course. Sure, the concept of equilibrium is a topic mentioned and identified throughout the course however the dialogue in regards to conditions that would shift the chemical system is minimal at best.
I recently stumbled across a blog about the use of BCA (Before Change After) tables for stoichiometry written by Lowell Thomson. I was thrilled to discover ChemEd Xchange! I wanted to share my journey, spurred on by my students, into the extensive use of the BCA approach in AP and
This Activity explores factors that influence dynamic equilibrium, including how long it takes two populations to equilibrate, and the relative amounts of reactants and products present at equilibrium. Students first use concrete objects (coins), then progress to mathematical calculations of equilibrium without physically manipulating the objects.
The liquefaction of carbon dioxide is shown. In Part 1, dry ice is placed in a strong plastic tube and a pressure gauge is attached.
The liquefaction of carbon dioxide is shown. In Part 2, the valve is closed and the pressure in the tube builds until all three phases of carbon dioxide are present.
The liquefaction of carbon dioxide is shown. In Part 3, the pressure in the tube continues to rise until the valve is opened, at which point the pressure drops and the liquid changes to solid.