CHEM 106 1st EditionExam # 2 Study Guide Lectures: 15,16,21Exam 2 Breakdown: Chapter 15 ~ 10 QuestionsChapter 21 ~ 6 QuestionsChapter 16 ~ 7 QuestionsExperiment 14 ~ 1Chapter 15: Chemical KineticsReaction Rate = ∆[ ]∆ tt = time∆ []=[ ]final−[ ]initialRules: always positive, can be based on any product or reactant, adjust for stoichiometryAs a reaction proceeds, average rate decreases Reaction rate ↓ as t ↑ Reaction progresses more quickly when [ ] of reactants is higherArrhenius Equation: k = A e-Ea/RTk: rate constant A: frequency factor Ea: activation energyR = 8.314 T = KelvinPotential energy: bond strength Kinetic energy: energy of motionSuccessful reactions convert KE to enough PE to overcome the required Ea Fitting data to the Arrhenius equation: ln (k) = ln (A) –Ea/R (1/T)Elementary Steps: individual steps in a mechanismIntermediate: produced in one step and consumed in the nextMolecularity: number of molecules in an elementary stepUnimolecular: A → B rate = k [A]Bimolecular: A + A → C rate = k [A]2 A + B → C rate = k [A][B]Rate determining step: slowest of the two elementary steps, controls reaction ratePlots: time vs. [A] – if linear, then zeroth ordertime vs. ln [A] – if linear, then 1st ordertime vs. 1/[A] – if linear, then 2nd orderChapter 21: Nuclear & RadiochemistryXZAX = element A = mass #, p + n Z = atomic #, protonsSmaller nuclei:p11=protonn01=neutronβ+10=positronβ−10=negatronAlpha particle:α24 or He24Deutron: n + p:H12 or d12Fusion reaction:Fe + α → ¿2860242656Neutron Capture:Fe +3 n012656→ Fe2659Negatron Decay:X 1→ X 2+ β−¿+´vZ+1AZA¿-will occur in neutron rich isotopesPositron Decay:X 1→ X 2+ β+¿+vZ−1AZA¿Ex: Isotope of Kr (z=36) undergoes β decay, what element is produced? Z=37RbRadioactive Decay: Nt = No e-RtNo=# nuclei at t =0 Nt=# nuclei at t n=# half livesNuclear binding energy: change in mass when 2 nuclei fuseΔm = mass difference = (mass of free nuclear particles) – (mass of nucleus)BE = Δmc2 (then for 1 mole of atoms multiply by Avogadro’s #)Measuring Radioactivity: # decay events/unit time = radioactivity1 disintegration/second = 1 dps 1 dps = 1 Bq BecquerelA = k N A = activity k = rate constant (dps) N = # atomsHow many atoms, moles, and grams in 106 Bq of 223Ra? (Solve for N)→ N = A/kRadioactivity Penetrating Power:α , β−kinetic energyγ− photon;wavelengthShielding:α – not very penetratingβ – more penetrating than αγ – very penetratingRadiometric Dating: carbon dating – 14C → 14N + β +´v−10Measure amount of 14C decay relative to 12C14C/12CPractice problems such as “If the 14C/12C ratio equals 30% of value for a living organism, how old is the basket?”Chapter 16: Chemical Equilibria At equilibrium, the reaction has not stopped, it is still occurring Forward reaction rate is equal to the reverse reaction rate So Kf [ ] = Kr [ ] then Kf/Kr = K (capital K)K is the equilibrium constant and is always [products] over [reactants]Law of Mass ActionaA + bB ↔ cC + dD Kc = D¿d¿B ¿bA ¿a¿¿C ¿c¿¿¿(products over reactants)Kc is based on molarity/concentration while Kp is based off of partial pressures (gases)Ptotal = P1 + P2 + P3… Kp = PD¿d¿PB¿bPA¿a¿¿PC¿c¿¿¿(units are not needed) (value of Kp ≠ Kc)When K > 1 – products are in excess When K < 1 – reactants are in excessIf Kc = 1 – neither products or reactants are favoredIf Kc > 1 – products are favored, equilibrium lies to the rightIf Kc < 1 – reactants are favored, equilibrium lies to the lefRelationship between Kc and Kp: Kp = Kc (RT)Δn(Δn is products – reactants)Note: R = 0.08206The forward reaction and reverse reaction have a reciprocal relationship: Kr = 1/KfWhen equilibrium is multiplied by some factor, you raise the concentration to that same factor → 2A ↔ 2B goes to K2 = [B]2/[A]2 (2 is the factor here)When you combine reactions, it is just like Hess’s Law except when you reverse a reaction to fit your equation; you take the reciprocal of that K value (instead of just making it negative). Also, when you multiply a reaction by a factor of 2, the K value must then be raised to that same factor (instead of just multiplied).Reaction Quotient (Q) is the value for mass action at any concentration (doesn’t have to be at equilibrium) at equilibrium, Q = KIf Q < K, need more products, less reactants, shifs equilibrium to the rightIf Q > K, need more reactants, less products, shifs equilibrium to the lefWith heterogeneous equilibrium, pay attention to phases in reactions. If it is a solid or liquid, it can be lef out of the calculations because its concentration is 1. (there are extensive example problems provided in the book)Le Chatelier’s Principle: if a system at equilibrium is perturbed it will respond to get back to equilibrium (qualitative)Comparing Q vs K (quantitative)(there are several longer examples in the