CHEM 102 1nd Edition Lecture 17 Outline of Last Lecture I. Rate Determining StepII. Guidelines for Constructing MechanismsIII. Mechanisms with Fast First StepsIV. CatalystsOutline of Current Lecture I. Heterogeneous CatalystsII. EnzymesIII. Chemical EquilibriumIV. Homo- vs Hetero- V. Properties of Kc vs k VI. Magnitude of KCurrent LectureI. Heterogeneous Catalystsa. Heterogeneous catalysts are a different phase from the reactantsb. The Larger the surface area, the greater the effectivenessII. Enzymesa. Proteins that catalyze specific biochemical equations b. They can be homogeneous or heterogeneous catalystsc. They can increase the rates by 108 to 1020d. Example 1i. Presence of enzyme causes:ii. E + S ES (fast, eq)iii. ES EPiv. EP E + Pv. What is the rate law?1. k[S]2. k[E][S]****3. k[E]4. k[ES]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.5. Because; k2 = k[ES] where [ES] equals [E][S] because of the first reaction.e. Example 2i. What is the overall rate law: 2O3 3O2?ii. Proposed mechanism:iii. O3 O2 + O (fast)iv. O + O3 2O2 (slow)1. k[O3]2. k[O3]2/[O2]****3. k[O][O3]4. [O3]2[O]5. Because; k2 = k[O][O3] where [O3] = [O][O2], so, [O] = [O3]/[O2]III. Chemical Equilibriuma. Reactions never complete or are used fullyb. The reaction is in chemical equilibrium instead because in the reaction, the products and the reactants in equilibriumc. The equation goes forward and reverse at the same rated. For the general equation: aA + bB cC + dDe. The equation at any given temperature = Kc = [C ]c[ D ]d[ A ]a[B ]bf. At equilibrium, the concentrations are not equal, but the rates areIV. Homo- vs Hetero- a. A homogeneous reaction is a single-phase reactioni. The catalyst will be the same phase as everything elseb. A heterogeneous reaction is a multiple-phase reactioni. The catalyst will be a different phase as everything elseii. 2 HgO (s) + 2 Hg (l) + O2 (g)iii. Liquids and solids are not included in the overall rate; therefore, Kc = [O2] and the reverse reaction’s rate would equal 1/[O2]V. Properties of Kc vs k K equilibrium K reaction rateDimensionless quantity NoReaction specific YesOnly good at specific temperature YesVI. Magnitude of Ka. Measure of the extent of concentrationb. Dependent on nature and temperature of reactionc. K >1, mainly product heavyd. K <1, mainly reactant heavye. K ~ 1 prod ~
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