Chemistry Outcomes Review: Chapter 9
Chemical Equilibrium
Many chemical systems that appear unchanging have reached a state of equilibrium where the forward and reverse reactions that characterize their chemistry are going at the same speed. We cannot detect any net change by observing these systems, but the reactions continue at the molecular level; equilibrium is dynamic. Le Chatelier's principle states that, if we disturb an equilibrium system by changing one or more concentrations or adding or subtracting energy, the system responds in a way that minimizes the disturbance. The equilibrium constant and equilibrium constant expression provide ways to quantify this qualitative (directional) principle and we applied them to acid-base and solubility equilibria.
We connected the equilibrium constant to the thermodynamic variables introduced in the previous two chapters and found that this combination allows us to calculate equilibrium constants from thermodynamic data alone and conversely to use equilibrium measurements to obtain thermodynamic data. A particularly useful result of these connections is the ability to analyze the temperature dependence of equilibria quantitatively.
Check your understanding of the ideas in this chapter by reviewing these expected outcomes of your study.
You should be able to:
- Use Le Chatelier's principle to predict the direction of the response of an equilibrium system to changes in the concentration(s) of reactants or products [Sections 9.1, 9.3, 9.4, 9.5, and 9.6].
- Use Le Chatelier's principle and the response of an equilibrium system to heating or cooling to tell whether the reaction is endothermic or exothermic [Sections 9.1 and 9.8].
- Explain how Le Chatelier's principle is a consequence of the dynamic nature of chemical equilibrium [Section 9.1].
- Write the equilibrium constant expression, using appropriate "concentration" units, for a balanced chemical reaction [Sections 9.2, 9.6, and 9.7].
- Find Ka and pKa for a weak acid when you have the initial concentrations in the solution and the pH at equilibrium [Sections 9.3 and 9.4].
- Find the pH of a solution of a weak acid or its conjugate base when you have the initial concentrations in the solution and the Ka or pKa for the acid [Sections 9.3 and 9.4].
- Find the concentrations of a weak acid and its conjugate base in a solution when you have the initial concentrations in the solution and the Ka or pKa for the acid [Sections 9.3, 9.4, and 9.5].
- Find the pH of a buffer solution when you have the initial concentrations of the weak acid and its conjugate base in the solution and the Ka or pKa for the acid [Section 9.4].
- Tell how to prepare a buffer solution of a specified pH and specified total concentration of an appropriately selected weak acid-base conjugate pair [Section 9.4].
- Predict the direction of change of the net charge on a protein and its consequent behavior in electrophoresis if one amino acid is substituted for another in its structure [Section 9.5].
- Find the solubility product, Ksp and pKsp, for an ionic compound when you have data for the solubility of the compound and vice versa [Sections 9.6 and 9.8].
- Find the solubility of an ionic compound of known Ksp or pKsp in a solution containing a stoichiometric excess of one of the ions [Section 9.6].
- Find ∆G°reaction for a reaction when you have the equilibrium constant, K, for the reaction [Section 9.7].
- Find the equilibrium constant, K, for a reaction when you have ∆Gf° for the reactants and products [Sections 9.7 and 9.9].
- Find ∆H°reaction, ∆G°reaction, and ∆S°reaction for a reaction when you have calorimetric data for the reaction and its equilibrium constant, K [Section 9.8].
- Find ∆H°reaction, ∆S°reaction, and ∆G°reaction for a reaction when you have values of K for the reaction at two or more temperatures [Section 9.8].
- Find ∆G°reaction and K for a reaction at a temperature T when you have ∆H°reaction for the reaction [Section 9.8].
- Find the free energy ∆Greaction for a reaction that is not at equilibrium when you have ∆G°reaction or K for the reaction and the concentrations in the non-equilibrium system [Section 9.9].
- Find ∆G°reaction or ∆Greaction for a coupled reaction when you have ∆G°reaction or ∆Greaction for the individual reactions that are coupled [Section 9.9].