These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute. Outline of Last Lecture I. Concept of Equilibrium Concentrations II. Law of Mass Action III. Equilibrium Constant Outline of Today’s Lecture I. Equilibrium Constant, K II. Relationship between K and G III. Equilibrium Response to Change Today’s Lecture Equilibrium constant, K: 1. Write the equilibrium constant expression for CaCO3 (s) CaO (s) + CO2 (g): K = PCO2 (Because solids are not expressed in the equilibrium constant expression) 2. Write the equilibrium constant expression for Ca(OH)2 (s) Ca 2+ (aq) + 2 OH- (aq) K = [Ca2+][OH-]^2 (Remember that solids are not shown in the expression) 3. Calculate Kc given Kp for N2 (g) + 3 H2 (g) 2 NH3 (g) Kp = (RT)^n Kc N = 2 -4 (moles of gas) Kc = Kp (RT)^2 The relationship between K and G: - Pure products (in standard state) are lower in free energy - Equilibrium is achieved at minimum free energy - Delta G difference in molar free energy of products and reactants at any definite fixed composition of reactants and products - DG = DG° + RT ln Q at equilibrium - Q = activities of products divided by activities of reactants - Q is the reaction quotient (tells us where on the reactant path we are located) - Q = K, DG° = 0 - DG = -RT ln K MEMORIZE THIS! o Therefore K depends on G Equilibria Response to Change: Le Chatelier’s Principle states that when a stress is applied to a system in dynamic equilibrium, the equilibrium tends to adjust to minimize the effect of the stress - Types of stress: CH 302 LaBrake, Cynthia 2013 Spring Week 5 Lecture 9 February 12, 2013o Adding or removing reagents When you add reactant, reaction shifts right When you remove product, reaction shifts right When you add product, reaction shifts left o Changing volume of gas phase Compression: composition will change in a way that minimizes the resulting increase in pressure Expansion: composition will change in a way to increase the pressure Inert Gas: No effect on Q so no shift at constant volume When you increase pressure (compress), reaction moves towards side with fewer gas moles o Adding or removing heat Exothermic reactions, heat is like a product so when temperature increases, reaction shifts to the left Endothermic, temperature increases and k increases so heat is like a reactant and shifts to the
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