Thermodynamics

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Unformatted text preview: en the experimentally determined rate law, determine the correct reaction mechanism given possible mechanisms molecularity of a reaction – unimolecular, bimolecular, termolecular – Explain why unimolecular and bimolecular steps are common but termolecular steps are very rare – Determine the corresponding rate law for a given elementary step intermediate: species produced in an earlier step and consumed in later step of mechanism Distinguish between a catalyst and an intermediate – Be able to identify the correct mechanism for a reaction given information on any catalysts, intermediates, rate laws, and/or reaction orders CHAPTER 14: THERMODYNAMICS system: that part of the universe being studied surroundings: the rest of the universe outside the system CHEM 162 Exam 3 Review 1st Law of Thermodynamics: Energy is neither created nor destroyed. page 2 of 4 CHAPTER 14: THERMODYNAMICS Enthalpy change, H = qreaction at constant pressure (e.g atmospheric pressure) – endothermic reaction: H = + – energy of reactants < energy of products; surroundings feel cooler after reaction; – for physical changes, products have higher kinetic energy than reactants – exothermic reaction: H = – – energy of reactants > energy of products; surroundings feel hotter after reaction; – for physical changes, products have lower kinetic energy than reactants nonspontaneous process: only occurs with external intervention or stimulus Entropy, S: measure of randomness factor – Ssolid < Sliquid < Sgas – S=0 only for a perfect crystalline solid at 0K (3rd Law of Thermodynamics) – S > 0 for all other substances, even naturally occurring elements; the more complex the molecule the greater its absolute entropy, S°. – Recognize S is positive for a reaction that increases the # of moles of gas particles. – Recognize if Ssys increases or decreases based on increased kinetic energy or changes in physical state. Calculate S° given S° data Suniv = Ssys + Ssurr 2nd Law of Thermodynamics: For any spontaneous process, the Suniv increases. H sys T Definitions of standard state 1. A gaseous substance with P=1 atm 2. An aqueous solution with a concentration of 1M at a pressure of 1 atm 3. Pure liquids and solids 4. The...
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