Chemistry: Rate Laws and Kinetics, Study notes of Chemistry

Download Chemistry: Rate Laws and Kinetics and more Study notes Chemistry in PDF only on Docsity! Turn on Camtasia Recording! 1... 1.Concentrations (Mg in HCl) Factors Affecting Rates 2. Physical state of reactants and products (eg. Lycopodium powder) 3. Temperature (hot bleach) 4 C t l t ( t t & H O ) 2 . a a ys s po a o 2 2 (MnO2 & H2O2) ... Interpreting Rate Laws Rate = k [A]m[B]n If m = 1, rxn. is 1st order in A If [A] doubles, then rate goes up by factor of __ If m = 2, rxn. is 2nd order in A. Doubling [A] increases rate by ________ 3 If m = 0, rxn. is zero order. If [A] doubles, rate ________ ... What is the rate law for this reaction? 2NO(g) + Cl2(g) --> 2NOCl(g) A. Rate = k [NO]2 4 B. Rate = k [NO]2 [H2]1 C. Rate = k [NO]2 [Cl2] D. Rate = k [NOCl]2 ... Concentration / Time Relations Integrating -(A [R] / A time) = k [R], we get Dn CJ - kt [F wdew a \ wtegaled CK. Dn @&- MR, = -Aet &. WR +n Reo fraction remaining after time t has elapsed. Bee Re -—gPARe “4 Re = z cE order witeqrated wale lw a? IRI/IRlo = x& sn +b Summary of Rate Laws 1 Table 15.1 Characteristic Properties of Reactions of the Type“R —> Products” Rate Integrated Rate Straight-Line Orde\_ Equation Equation Plot. Slope —k Units 0 Rate —A[RI/AT= {RP [RJo - [Rk=K 1 ales -A[R/AT= e in (RR) =~ 2Wdie= —A[RI/AT= KR RD (4/[R Jo) =e aR ERS = Q-\k = het ay = kt +Re = + MnRe gas Got dBi) eu vs. t -k mol/L + time In [R}. vs. t -k time A [R], vs. t k L/mol - time ®@ ar r 8 Integrated Rate Laws For the general reaction R → P, if [R]0 is the starting concentration of R and [R]t is the concentration at time t, Reaction order in R: Rate Equation Integrated Rate Law First Order −Δ[R] Δt = k[R] −Δ[R] 2 ln [R]t [R]0 ⎛ ⎝ ⎜ ⎞ ⎠ ⎟ = −kt 1 1 11 Second Order Zero Order Δt = k[R] −Δ[R] Δt = k[R]0 = k [R]t − [R]0 = kt [R]0 − [R]t = kt ... Reaction Rate Constants Zero order reaction: First order reaction: 12 Second order reaction: ... Concentration / Time Relations Sucrose decomposes to simpler sugars like glucose Rate of disappearance of sucrose = k [sucrose] If k = 0.21 hr-1 and [sucrose] = 0.010 M How long to drop 90% (to 0 0010 M)? 13 Glucose . ... U th fi t d i t t d t l Rate of disappearance of sucrose = k [sucrose]. k = 0.21 hr-1. If initial [sucrose] = 0.010 M, how long to drop 90% or to 0.0010 M? se e rs or er n egra e ra e aw 14... What is the rate order for a reaction where the data l k likoo e: A.Zero B.First 19 C.Second D.Fourth ... What is the rate order for a reaction where the data l k likoo e: A.Zero B.First 20 C.Second D.Fourth ... What is the rate order for a reaction where the data l k likoo e: A.Zero B.First 21 C.Second D.Fourth ... Half-Life of Reaction HALF-LIFE is the time it takes for 1/2 a sample is disappear. For 1st order reactions, 22 the concept of HALF-LIFE is especially useful. ... Reaction is 1st Half-Life order decomposition of H2O2. 23... Half-Life Reaction after 1 half-life. 1/2 of the reactant has been consumed and 1/2 24 remains. ... Half-Life S l ti Rate = k[sugar] and k = 3.3 x 10-4 sec-1. What is the half- life of this reaction? o u on [R] / [R]0 = fraction remaining when t = t1/2 then fraction remaining = _________ 29... Half-Life If rate = k[sugar] and k = 3.3 x 10-4 sec-1 and the half-life is 35 min. Starting with 5.00 g sugar, how h i l ft ft 2 h d 20 i (140 i )? Solution 2 hr and 20 min = 4 half-lives Half-life Time Elapsed Mass Left muc s e a er r an m n m n 30 1st 35 min 2.50 g 2nd 70 1.25 g 3rd 105 0.625 g 4th 140 0.313 g ... Half-Life Radioactive decay is a first order process. Tritium ---> beta + helium 3H ---> beta + 3He 31 Carbon-14 decay: 14C ---> beta + 14N ... Half-Lives of Radioactive Elements Rate of decay of radioactive isotopes given in terms of half-life. 238U --> 234Th + He 4.5 x 109 yr 14C --> 14N + beta 5730 y 131I --> 131Xe + beta 8.05 d 32... The decomposition of phosphine, PH3, proceeds according to the equation below. It is a first-order process The half life is 37 9s . . at 120°C. How much time is required for 3/4 of the material to decompose? 4PH3 (g) --> P4 (g) + 6 H2 (g) A. 37.9 s 33 B. 79.8 s C. 120 s D. 113.7 s ... The decomposition of phosphine, PH3, proceeds according to the equation below. It is a first order process The half life is 37 9s - . . at 120°C. What percentage of the sample remains after 1 minute? 4PH3 (g) --> P4 (g) + 6 H2 (g) A. 0.421 34 B. 0.382 C. 0.335 D. 0.212 ...