Lesson # 1 Equilibrium Systems Chemical Equilibrium Lesson # 1 Equilibrium Systems VIDEO (first 4 mins)

Reaction Completion vs. Equilibrium In open systems, most reactions go to completion. The reactants are used up and the products are formed, and that’s it. In closed systems, it is possible for reactions not to go to completion, but rather to equilibrium, where the concentration of the reactants and products are constant, and the rate of the forward reaction is equal to that of the reverse reaction. These reactions are considered to be in dynamic equilibrium. The equilibrium position is the point at which the relative concentrations of the reactants and products stop changing. rf = rr

Dynamic Equilibrium Equilibria are dynamic (reactants form into products and vice versa) until the system is disturbed in some way (the addition of more reactants, removal of products, change the temperature, pressure, etc.) Reversible reactions can proceed in both the forward and reverse directions, setting up an equilibrium in a closed system. Even reactions that go to completion are still considered reversible, it is only that quantitatively, 99% will favour the products.

Equilibrium Reaction Progress

ICE Charts Stoichiometric calculations are used to determining equilibrium concentrations using an ICE chart. I – initial concentration C – change in concentration E – equilibrium concentration

Example 1 Hydrogen fluoride is used in the production of many important substances, including medicines. It may be synthesized from gaseous hydrogen and fluorine: H2 (g) + F2 (g) = 2 HF (g). When a chemist starts this reaction, the initial concentration of both reactants are 2.00 mol/L. No hydrogen fluoride gas is present initially. What are the equilibrium concentrations of hydrogen and hydrogen fluoride, if fluorine gas has an equilibrium concentration of 0.48 mol/L?

Example 2 When ammonia gas is heated, it composes to form nitrogen and hydrogen gas: 2 NH3 (g) = N2 (g) + 3 H2 (g). A chemical adds 2.0 mol/L ammonia to a sealed container and heats it. Determine the equilibrium concentrations of N2 and H2 if the equilibrium concentration of ammonia is 1.0 mol/L.