CHEM 102 1st EditionExam # 1 Study Guide Lectures: 7 - 13Lecture 1 (September 19)- At 25 degrees C: 3NO (g)  N2O (g) + NO2 (g)o We want to know if this reaction is spontaneous (delta S universe = delta S system + delta S surroundings  Delta S system = (-delta H rxn/T) Delta S system = -172.4 J/Ko Delta S surroundings: 3NO (g)  N2O (g) + NO2 (g) Delta Hf: 90.25 82.05 33.2 Delta H rxn: (82.05 + 33.2) – 3(90.2) = -155 kJ Delta S surroundings: -(-155 kJ)/298.15 = 0.5125 kJ/Ko Delta S universe = -172.4 J/K + 5215 J/K = 349.1 J/K- Gibbs Free Energy, Go G: thermodynamic state function State function indicates amount of energy available for a system to do useful worko Delta G: maximum amount of useful work that can be done by reaction at constant T,P state function (kJ/mol) Delta G calculate from delta Gf 298 (in tables)- Delta Gf = 0- Delta Hf = 0- Delta Sf does not equal zero for elements in standard state - Delta G reaction indicates spontaneity o Delta G < 0forward reaction spontaneous o Delta G > 0forward reaction is NOT spontaneous but reverse reaction IS spontaneous o Delta G = 0  reaction is at equilibrium Reactantsproducts just as fast as productsreactants- 3NO (g)  N2O (g) + NO2 (g)86.54 104.2 51.3o Delta G reaction = (104.2+51.3) – 3(86.54) = -104 kJo Negative so reaction is spontaneous at 25 degrees C (because data in table is at 25 degrees C)- Gibs Helmhots equationo Delta G reaction = delta H reaction – T(delta S reaction)o For 3NO (g)  N2O (g) + NO2 (g) Delta G reaction = delta H reaction – T(delta S reaction) Delta G reaction = 755 kJ – (298.15 K)(-0.1724 kJ/K) = -104.1 kJLecture 8 (September 24) - Gibbs free energy change for a reactiono Delta G reaction = delta H – T(delta S) When you sue data from tables, T=298.15K (25 degrees C) You are figuring out if reaction is spontaneous at 25 degrees C Delta G reaction < 0  spontaneous Delta G reaction > 0  non spontaneous for forward reaction- Reverse reaction is spontaneous Delta G = 0  equilibrium- Reaction A  B o Delta G < 0: reaction will proceed to produce products, more B is made until equilibrium is reachedo Delta G > 0: reaction proceeds forward reactants, more A is made until equilibrium isreachedo Detla G = 0: you are at equilibrium, A is converting to B just as fast as B is converting to A A  B- How to create a spontaneous reactiono –Delta G, -delta H, +T(delta S) Reaction spontaneous at T, exothermic, more disordero –Delta G, -delta H, T(delta S) Reaction spontaneous at low T, exothermic, less disordero –Delta G, +delta H, +T(delta S) Reaction spontaneous at high T, endothermic, more disordero +Delta G, +delta H, -T(delta S) Delta G will ALWAYS be positive (forward reaction will be non spontaneous at all G), endothermic, less disorder- Chemical kineticso Thermodynamics is used to predict if reaction will proceed in forward reaction o Cannot tell you how fast the reaction will go o Study of rates of chemical reactions (determining how fast reactions and mechanisms as which they happen)o Mechanism: the order in which bonds are formed and broken as reaction proceeds o Rate: change in concentration of a product on reactant per unit time Always positive  Reactant over time decreases while the product increases in amount of concentrationLecture 9 (September 26)- Rate of reaction depends on four factorso Nature of reactantso Concentration complicatedo Temperature o Catalysts - Nature of reactantso Chemical activity where e- are  2Na (s) + 2H2O  2NaOH (aq) + H2 (g)o Physical nature: Aqueous species react faster than gases species  Size of particles of solids surface area- Concentration complicatedo Rate law expression-form from experimental datao R=k([A]) where k=rate law constant and [A]=concentration of A Units are (M/t) or molarity/timeo Most reactions are not 1 step therefore we need to do experimentso Aa + Bb  Cc + Dd Reactants  productso Rate law expression Rate (M/t) = k[A]x[B]y- K=specific rate constant- A and B=fractions- X=order of reaction with respect to A- Y=order of reaction with respect to B Lecture 10 (October 1)- Rate of reaction depends on four factorso Nature of reactantso Concentration complicatedo Temperature o Catalysts - Nature of reactantso Chemical activity where e- are  2Na (s) + 2H2O  2NaOH (aq) + H2 (g)o Physical nature: Aqueous species react faster than gases species  Size of particles of solids surface area- Concentration complicatedo Rate law expression-form from experimental datao R=k([A]) where k=rate law constant and [A]=concentration of A Units are (M/t) or molarity/timeo Most reactions are not 1 step therefore we need to do experimentso Aa + Bb  Cc + Dd Reactants  productso Rate law expression Rate (M/t) = k[A]x[B]y- K=specific rate constant- A and B=fractions- X=order of reaction with respect to A- Y=order of reaction with respect to BLecture 11 (October 3)- Reaction mechanism and rate law expression o Series of steps that takes the reactants and turns them into productso Unomolecular decomposition (A  B+C)o Bimolecular collision (A + B  C) Trimolecular collisions are VERY rareo The slowest step controls the overall reaction Called the rate determining step  Step with the highest activation energyo The experimentally derived rate law expression is tightly connected to the slow step of the mechanism- Exampleo 2A + B + C  AC + AB Rate law expression=k [A]x [B]y [C]zo After doing experiment, rate = k [A][B][C]o Concentrate on slow step and ignore all steps afterward Rate = k[A]2 where 2 is the number of times A appears as a reactant - Not the mechanismo A2 is an intermediate as it is neither a reactant nor product It was formed and then destroyed- Effective temperature o 1 step reaction A + B  C (rate = k[A]1[B]1)- Exothermic, not dependent on temperature As T increases, energy of molecules increases- More molecules have necessary energy to create transition state and ultimately form productsLecture 12 (October 8)- Effects of catalysto Catalysts are substances that speed up reactionso They can appear in an equation A + B + catalyst  C + catalyst A + B  Co Catalysts lower the Ea of rate of determining step (slow step) Catalysts lower Ea by getting involved in reaction and