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This 3 page Class Notes was uploaded by BettyAnn Mead on Friday February 6, 2015. The Class Notes belongs to 112 at University of Massachusetts taught by Voigtman in Spring2015. Since its upload, it has received 52 views.
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Date Created: 02/06/15
k1 0 Means AHO Neither product or reactant favored kgtgt1 Means AHltO o Exothermic Product favored kltlt1 Means AHgtO o Endothermic Reactant favored Reaction Mechanism The sequence of bondbreaking and bond making steps that are involved in the conversion of reactants to products 0 Can be VERY complicated Most reactions involve multiple simple steps Each of the steps is called an elementary step because it involves a single molecular event such as bondbreaking and bondmaking Types of Elementary Steps Unimolecular A Products Bimolecular AA Products AB Products Termoecuar AAA Products AAB Products ABC Products Slow and Fast Steps 0 Products can never be produced at a faster rate than the slowest step 0 The slowest step is called the ratelimiting step 0 If multiple steps are involved then the rate equation is determined from the slowest step 0 If two or more steps are involved and the FIRST step is the slow step then the rate equation is determined by the FIRST step 0 If there are two steps an the SECOND step is slow then 0 Ratelimiting step 0 Rate equation is based on the SECOND step 0 No intermediates can appear in the rate equation 0 At equilibrium in the rst elementary step Rate of Forward ReactionRate of Reverse Reaction 0 There is no simple way to know if a plausible reaction mechanism is what actually happens in reality Some Rules for K Expressions 0 Products in numerator and reactants in denominator o The exponents are the stoichiometric coef cients Law of Mass Action 0 K is both reaction and temperature but NOT catalyst dependent o Ignore the units Solids do not appear in K expressions 0 Water if in excess does not appear in K expressions PVnRT For Ideal Gas gas concentrationPRT Antotal moles of product total moles of reactant KKRTquotAn What do K values mean K0 o K10 No forward reaction 0 Means no reaction Reactant favored Kinfinity o K 10 o No reverse reaction 0 Means no reaction 0 Product favored Kltlt1 Reactant favored Kgtgt1 Product favored The Reaction Quotient Q aAbB l cCdD Reaction QuotientQCquotcDquotdAquotaBquotb o This is not K 0 K is a special case of Q If you change the temperature of the concentration of reactants or products it attempts to return to equilibrium unless perturbed so much it cannot return to equilibrium AT EQUILIBRIUM ONLY l KQ If Q K the system is NOT at equilibrium 0 If QltK there is too much reactant and too little product If QgtK there is too much product and too little reactant
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