Q-Kinetics Prem Sattsangi Copyright 2009 http://jchemed.chem.wisc.edu/JCEsoft/cca/cca3/main/clockrx/page1.htm

#2-Chemical Kinetics: (p.574) Study of the Rate of a Chemical Process Reactions happen because, molecules collide with each other. Reactions proceed faster, if the following are increased: 1. Reactant concentration. [Increased concentration, more collisions per second.] 2. Temperature. [Faster moving molecule, more collisions per sec.]

#3-Average rate (M/s) (p. 576) Time (s) [C4H9Cl] (M) 0.0 0.1000 100 0.0820 200 0.0671 Calculate average rate between 100 sec -200 sec Av. Rate =- {[0.0671]final – [0.0820M]init.} 200 secfinal – 100 secinitial = 1.49 x 10-4 M/s

#4-Rate and Stoichiometry (p. 579) Reactants  Products N2(g) + 3H2(g)  2NH3(g) As reaction proceeds, concentration of: Reactants decrease (minus sign), -D[R]/Dt Products increase, D[P]/Dt To equate the rates, divide by the coefficient, in the balanced equation.

#5-Study of Reaction Rate as a function of Concentration at 25oC (p #5-Study of Reaction Rate as a function of Concentration at 25oC (p. 580) [one reagent a a time] Reactants Products NH4+(aq) + NO2-(aq)  N2(g) + 2H2O(l) No. [NH4+] [NO2-] Rate Constant 1. 0.0100 0.200 5.4 x 10-7 2. 0.0200 0.200 10.8 x 10-7 Doubling the [NH4+] doubles the rate. 3. 0.200 0.0202 10.8 x 10-7 4. 0.200 0.0404 21.6 x 10-7 Doubling the [NO2-] doubles the rate.

#6-Rate Law Equation (p. 581) Rate = k [NH4+]1 x [NO2-]1 “k” = Rate constant, (Value increases at higher temperature.) Exponents “1” are the order of reaction. This reaction is First order in NH4+ and First order in NO2- Overall reaction order = 1 + 1 = 2

#7-Figuring out Order of a reaction (p #7-Figuring out Order of a reaction (p.581) [Doubling Reactant Concentration] [R]r (order “r”) is related to Rate Doubling the concentration, “[2R]r” and its effect on Rate: Rate Equation “r” Order UNCHANGED [2R]0 = 1 x Rate “0” 2 x [2R]1 = 2 x Rate “1” 4 x [2R]2 = 4 x Rate “2” 8 x [2R]3 = 8 x Rate “3”

#8-Figuring out Order of a reaction [Tripling Reactant Concentration] [R]r (order “r”) is related to Rate Tripling the concentration, “[3R]r” and its effect on Rate: Rate Equation “r” Order UNCHANGED [3R]0 = 1 x Rate “0” 3 x [3R]1 = 3 x Rate “1” 9 x [3R]2 = 9 x Rate “2” 27 x [3R]3 = 27 x Rate “3”

#9-Orders (0, 1, 2, or 3) Trial [A](M) [B](M) Rate (M/s) 1 0.273 0.763 2.83 x 10-6 2 0.273 1.526 2.83 x 10-6 3 0.819 0.763 2.547 x 10-5 In 1 and 2 [A] is constant, [B] is doubled Rate remained same, Order in B = 0 In 1 and 3 [B] is constant, [A] is tripled Rate changed to 9 x or 32. Order in A = 2

#10-Calculating the value of “k” (p. 581) at 25oC NH4+(aq) + NO2-(aq)  N2(g) + 2H2O(l) No. [NH4+] [NO2-] Rate 1 0.0100 0.200 5.4 x 10-7 Rate = k [NH4+]1 x [NO2-]1 k = __Rate Ms-1___ = __ 5.4 x 10-7 Ms-1___ [NH4+]1 x [NO2-]1 [0.0100 M ]1 x [0.200 M]1 = 2.7 x 10-4 M-1s-1

#11 Units of “k” [M] in Rate (p. 581) cancels M in the denominator. Rate law k = Unit Rate = k[A]1 x [B]1 __Rate Ms-1___ M-1s-1 [A M]1 x [B M]1 Rate = k[A]1 x [B]2 __Rate Ms-1___ M-2s-1 [A M]1 x [B M]2 Rate = k[A]2 x [B]1 __Rate Ms-1___ M-2s-1 [A M]2 x [B M]1 Rate = k[A]2 x [B]2 __Rate Ms-1___ M-3s-1 [A M]2 x [B M]2

#12-Energy of activation Data: Set Temp(oC) time(s) D (T’) 23 (296K) (Dt’) 350 G (T) 13 (286K) (Dt) 650 (Average) Temperatures must be in K R= 8.31J/K.mol Ea = __________________ = 43.6 kJ/mol