CHEM271 Fall 2024 Lecture Notes PDF

Midterm I Average 69 % - 3/60 ↳ 41. pts CHEM271 Fall 2024 Lecture 13 Rate limiting steps, mechanisms, and catalysis Efrain E. Rodriguez University of Maryland Aurhenius k= exp() b frequen...

Midterm I Average 69 % - 3/60 ↳ 41. pts CHEM271 Fall 2024 Lecture 13 Rate limiting steps, mechanisms, and catalysis Efrain E. Rodriguez University of Maryland Aurhenius k= exp() b frequency EA = factor activation energy · E. E. Rodriguez, UMD, CHEM271 2 The two-point Arrhenius equation In k = (A E ⑰ - (nh-Ink E - ln k - = , 1 ⑨ 1/T (K-1) 10/16/2024 3 Example: Hydroxylamine decomposes to its products with a rate constant of 0.237 x10-4 L mol-1 s-1 at 0 °C. At 25 °C, its constant increases to 2.64 x10-4 L mol-1s-1. A. What is the order of the reaction? B. What is the activation energy for hydroxylamine decomposition? C. What is the frequency factor? NH2OHig + Ong) > - products & (6 mol"s" or M".s"( [NH - H023 # rate = k 2nd order 10/16/2024 4  Is In =C 7 Use R 8 314 Tz = 25 %, 298 15k. =. J no" K. T = 0 %, 273 15K. Ea = 6 52 X10"J. - mol " # = 65 2. 15 : molt 10/16/2024 5  for A factor ( solve (frequency + herelease InA = Ink In A = In (0 237x10"). + 6. 52x10 "T not -mot (27 In A = 18. 08 In A = 18 08. 18 08 A. = 2 =. x10 MT s. Reaction mechanisms from kinetics ↳ of reactants Sequence steps by which > - products Overall: NO2 (g) + CO (g) NO (g) + CO2 (g) Elementary steps: 1) NO2 (g) + NO2 (g) NO3 (g) + NO (g) 2) NO3 (g) + CO (g) NO2 (g) + CO2 (g) ↳) Write a rate for each elementary step. rate (step 1) k [N02]2(rate(step2) k[N0](0) = = 6 The molecularity of the rate laws Unimolecular Acg) products Most 3 > - probable Bimolecular A + A + molecularities. B + A - products B + B > - Termolecular A + A + B > - products 3 have 7 The rate-determining step (also Dr. Rodriguez’s commute on University Boulevard) ↳ The slowest elementary step is the rate-determing Step LD. The observed rate corresponds law to the rate-determining step. 10/16/2024 8 1) - 2 (log) (((g) 2) CH( > H((g) + ((z(g) - + * Cz(g) x() x(y + = , S) Find overall reaction intermediates Identify reaction of each step Determine molecularity.  1.) unimolec. C(y() > - 2x() ia Reaction & and Jy (g) : intermediates Short-lived and not in overall uxn Example: 2NO2 (g) + F2 (g) 2NO2F (g) 1) NO2 (g) + F2 (g) NO2F (g) +slow F (g) Elementary steps: 2) - F (g) + NO2 (g) NO2F (g) fast rate = k[NO2][F] bimdecular Fig) is ran intermediate. 9 10 1) NO2 (g) + NO2 (g) NO3 (g) + NO (g) 2) NO3 (g) + CO (g) NO2 (g) + CO2 (g) 11 Multi-steps involving an equilibrium k1 A (g) + B(g) C (g) + D (g) k-1 12 Example: I-(aq) + OCl- (aq) Cl- (aq) + OI- (aq) Elementary 1) OCl- (aq) + H2O (l) HOCl (aq) + OH- (aq) steps: 2) I- (aq) + HOCl (aq) HOI (aq) + Cl- (aq) 3) OH- (aq) + HOI (aq) HOI (aq) + Cl- (aq) 13  1) OCl- (aq) + H2O (l) HOCl (aq) + OH- (aq) 2) I- (aq) + HOCl (aq) HOI (aq) + Cl- (aq) 3) OH- (aq) + HOI (aq) HOI (aq) + Cl- (aq) a) Identify the reaction intermediates b) Identify the rate limiting step c) Propose a rate law for this based on answer b) 10/16/2024 14  1) OCl- (aq) + H2O (l) HOCl (aq) + OH- (aq) 2) I- (aq) + HOCl (aq) HOI (aq) + Cl- (aq) 3) OH- (aq) + HOI (aq) HOI (aq) + Cl- (aq) a) Identify the reaction intermediates b) Identify the rate limiting step c) Propose a rate law for this based on answer b) 10/16/2024 15