Chem 211 1st Edition Lecture 14 Outline of Last Lecture I. Collision Theory and ConcentrationII. Temperature and the Rate ConstantIII. Activation EnergyIV. Temperature and Collision EnergyV. Calculating Activation EnergyVI. Molecular Structure and Reaction RateVII. Transition State TheoryOutline of Current Lecture I. Reaction MechanismsII. The Rate-Determining Step of a ReactionIII. Correlating Mechanism with the Rate LawIV. Catalysis: Speeding up a ReactionV. EquilibriumVI. The Equilibrium ConstantVII. K and the Extent of ReactionCurrent LectureI. Reaction MechanismsA. The mechanism of a reaction is thesequence of single reaction steps thatmake up the overall equation.B. The individual steps of the reactionmechanism are called elementarysteps because each one describes asingle molecular event.C. Each elementary step is characterized by its molecularity, the number of particles involved in the reaction.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.D. The rate law for an elementary step can be deduced from the reaction stoichiometry – reaction order equals molecularity for an elementary step only.II. The Rate-Determining Step of a ReactionA. The slowest step in a reaction is the rate-determining or rate-limiting step.B. The rate law for the rate-determining step becomes the rate law for the overall reaction.III. Correlating Mechanism with the Rate LawA. A valid mechanism must meet three criteriaa) The elementary steps must add up to the overall balanced equation.b) The elementary steps must be reasonablec) The mechanism must correlate with the observed rate lawB. A mechanism is a hypothesis –we cannot prove it is correct, but if it is consistent with the data, and can be used to predict results accurately, it is a useful model for the reaction.IV. Catalysis: Speeding up a ReactionA. A catalyst is a substance that increases the reaction rate without itself being consumed in the reaction.B. In general, a catalyst provides an alternative reaction pathway that has a lower total activation energy than the un-catalyzed reaction.C. A catalyst will speed up both the forward and the reverse reactions.D. A catalyst does not affect either DH or the overall yield for a reaction.E. A homogeneous catalyst is in the same phase as the reaction mixture.F. A heterogeneous catalyst is in a different phase than the reaction mixture.V. EquilibriumA. Kinetics applies to the speed (or rate) of a reaction, the concentration of product that appears (or of reactant that disappears) per unit time.B. Equilibrium applies to the extent (or yield) of a reaction, the concentrations of reactant and product present after an unlimited time, or once no further change occurs.C. A system at equilibrium is dynamic on the molecular level; no further net change is observed becausechanges in one directionare balanced by changes in the other.D. This is also known as the LAW OF MASS ACTION.E. The values of m and n are those of the coefficients in the balanced chemical equation. Note that this is equilibrium, not kinetics. Therates of the forward and reverse reactions areequal, NOT the concentrations of reactants andproducts.VI. The Equilibrium ConstantA. Consider the reaction N2O4(g) >><<2NO2(g)B. The ratio of constants gives a new constant, the equilibriumconstantVII. K and the Extent of ReactionA. K reflects a particular ratio of product concentrations to reactant concentrations for a reaction.B. K therefore indicates the extent of a reaction, i.e., how far a reaction proceeds towards the products at a given temperature.C. A small value for K indicates that the reaction yields little product before reaching equilibrium. The reaction favors the reactants.D. A large value for K indicates that the reaction reaches equilibrium with very little reactant remaining. The reaction favors the