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UMass Amherst CHEM 261 - Enthalpy, Entropy, and Types of Organic Reactions
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Chem 261 1st Edition Lecture 13Outline of Last Lecture:I. Converting from 2D to 3D images reviewII. Chirality and Enantiomers reviewIII. MescompoundsOutline of Current Lecture:I. Classes of Organic ReactionsII. Equilibrium, Rates, and Energy ChangesIII. Enthalpy and EntropyClasses of Organic Reactions:Entropy (S): a measure of disorder of a systemEnthalpy (H): the sum of the internal energy of a system. The thermodynamic potential.1. Addition Reactions-2 molecules (starting materials) “adding” together to form one new end product. Results in an entropy gain (disorder)2. Elimination Reactions-1 molecule  2 molecules (split). Results in a loss in entropy (disorder)ΔS< 03. Substitution Reactions-involves the exchanging (at least) of parts of 2 molecules. There are always 2 reactants and 2 products. ΔS = 0, so no net change in the number of molecules4. Rearrangement Reactions-involves changing the connectivity between atoms/moleculesEquilibrium, Rates, and Energy Changes:aA + bBcC + dDKeq= [C] c [D] d[A]a[B]bGibbs Free Energy: favorability of a reaction to occur. ΔH = enthalpy (more defining of a reaction’s ability to proceed)ΔS = entropyΔG (Gibbs) = ΔH -T ΔS**where T is absolute temperature ( > 0 K)Enthalpy and Entropy: -computational chemistry can be used to predict terms for reactants to products-Does the energy it takes to break reactant bonds cost more than what you get back when you make a product bond?ΔH >0 , endothermicΔH < 0, exothermic**ΔH < 0, ΔS> 0 = favorable reactionΔG = -RT ln (Keq)**R = constant, 1.987 cal/kmol**ΔG°= standard conditionsKeq> 1, energy is released (exergonic/ exothermic , ΔH<0)Keq<1, energy is absorbed (endergonic/endothermic, ΔH> 0)Kinetics: speed of a reaction. Is harder to model/predictKrate=


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UMass Amherst CHEM 261 - Enthalpy, Entropy, and Types of Organic Reactions

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