Equilibrium reactions are those that are dynamic: the reaction can shift to form more reactants or more products depending on the physical or chemical conditions present. They were discovered and described empirically, but have a thermodynamic basis in the Gibbs Energy of the reaction. A reaction at equilibrium has both reactants and products present, and the rate of formation of products is equal to the rate of formation of reactants. A common application of equilibrium is the chemistry of aqueous acids. Acid strength is measured by the pH scale.
This unit could be a stand-alone unit, but I used it as the first day of a three-day series of in-class exercises designed to get students thinking about a real problem on the international space station that could be solved using equilibrium calculations.
1. Write the equilibrium constant expression from the law of mass action
2. Predict the response of a reaction at equilibrium to an external “stress”
3. Determine whether a given species is an acid or base
4. Calculate the pH of a solution of a weak acid in water
5. Write the chemical equation for the autoprotolyis of water
6. Calculate the solubility of a sparingly soluble salt
This was the first day of a 3-day equilibrium activity. The 2nd two days are presented in the linked activity entitled "Water reclamation on the ISS: "Houston, we have a problem."
Students worked problems in class or as homework. For our class, the problems were submitted electronically on Sakai.