# Shared Flashcard Set

## Details

Kinetics BLAHH
N/A
28
Chemistry
12/14/2014

Term
 What is the order of a plot of reactant concentration vs. time that has a straight line?
Definition
 Zero
Term
 What does not increase the value of the rate constant for a reaction?
Definition
 Increasing the [] of reactants
Term
 A certain reaction has an enthalpy of -75kJ and an Ea of 40kJ. A catalyst lowers the activation energy of the forward reaction by 15kJ. What is the Ea of the reverse reaction with the same catalyst?
Definition
 Ea=40kJCatalyst(-15)= 25kJReverse reaction(+75)=100kJ
Term
 What does a catalyst do?
Definition
 It increases the rate of the reaction and lowers the activation energy. (Makes the curve less steep.)
Term
 What is Ea?
Definition
 The minimum energy required to turn reactants into products.
Term
 At a certain temp., the first order decomposition of H202 exhibits these data:time (seconds, s)-015[H202] (mol L^-1)2.01.0At what time will the [H2O2]=0.50 mol L^-1?
Definition
 (This is first order, so you can't find the equation of the line). Concentration decrease by 1/2 every 15 seconds, so the concentration will be 0.50 after 30 SECONDS.
Term
 The rate of a reaction with just two reactants is observed to double when the concentration of one reactant is doubled and the second reactant is held constant. The rate is also observed to increase by a factor of nine when the concentration of the second reactant is tripled, holding the concentration of the first reactant constant. What is the overall order for this reaction?
Definition
 [A]^2[B]= order of 3
Term
 Tritium decays by a first-order process that has half-life of 12.5 years. How many years will it take to reduce the radioactivity of a tritium sample to 15% of it original value?
Definition
 t 1/2= 0.693/kk=0.05544ln(0.15)=-0.005544tt=34 yr
Term
 What step limits reaction rate?
Definition
 slowest
Term
 What is the overall order of a reaction with a rate constant having the units L•mol-1•s-1?
Definition
 Second
Term
 When reacted with water, the insecticides DDT decomposes with a half-life of 10 years. Approximately how many years will it take for 99% of a given sample to decompose once exposed to water in the environment?
Definition
 t 1/2= 0693/k10= 0.693/kk=0.0693ln(0.01)=-0.0693tt=70 yr
Term
 What, if decreased, will increase the rate of a reaction of a solid?
Definition
 Particle size
Term
 What reaction characteristic is changed by adding a catalyst to a reaction at constant temp?
Definition
 activation energy
Term
 Which statement is true for the general rate law: Rate = k[A]m[B]n? A)The exponents in the rate law must be positive integers. B)The values for the exponents must be determined by experiment. C)The overall order of the reaction is equal to m times n. D)It can be written from the stoichiometry of the overall reaction.
Definition
 C)
Term
 Does a catalyst lower the Ea for the forward reaction, reverse reaction, or both?
Definition
 Both
Term
 In the following reaction, what is the relationship between the rate of production of NH3 and rate of consumption of H2?N2(g)+3H2(g)=2NH3(g)
Definition
 -△[N2]/△t= (-1/3)△[H2]/△t = (1/2)△[NH3]/△t
Term
 For each of the following rate equations, describe what would happen to the rate if the concentration of reactant A was tripled and the concentration of reactant B is halved. a. Rate = k[A][B] b. Rate = k[A]2[B] c. Rate = k[A]2[B]2 d. Rate = k[A][B]3
Definition
 a. increases by 3/2 b. increases by 9/2 (3^2/2)c. increases by 9/4 (3^2/2^2)d. increases by 3/8 (3/2^3)
Term
 At 150C the decomposition of acetaldehyde CH3CHO to methane is a first order reaction. If the rate constant for the reaction at 150C is 0.029 min-1, how long does it take a concentration of 0.050 mol L-1 of acetaldehyde to reduce to a concentration of 0.040 mol L-1?
Definition
 ln[A]=-kt+ln(A0)ln(0.040)=-(0.029)t+ln(0.050)t=7.7 minutes
Term
 The decomposition of hydrogen iodide into hydrogen and iodine is a second order reaction. The rate constant k = 0.080 L mol-1s-1. How long does it take an initial concentration of 0.050 M to decrease to half this concentration?
Definition
 t 1/2= 1/k[A0]1/(0.080)(0.050)=250 seconds
Term
 The gas-phase decomposition of nitrous oxide has the following two-step mechanism.1) N2O = N2+O22) O+N2O = N2+O2Write the overall equation.Is O a catalyst or intermediate?Identify the lower step is the rate law = k[N2O].
Definition
 2N20 = 2N2+O2It is an intermediate because it was formed during the middle step of the reaction.Step 1 (less reactants)
Term
 As concentration increases, rate ________.
Definition
 Increases
Term
 What is the differential rate law for a zero order, first order, and second order reaction?
Definition
 Zero: r = k (unit= m/s)1st: r = k[A] (unit= s^-1)2nd: r = k [A]2 (unit= L/(mol•s)
Term
 What is the integrated rate law for zero, first and second order reaction?
Definition
 Zero- [A]=-kt+[A]01st- ln[A]=-kt=ln[A]0 2nd- 1/[A]= kt+ 1/[A]0
Term
 What are the rules of collision theory?
Definition
 •particles must collide•sufficient energy•correct orientation of particles
Term
 Find the overall reaction:Cl2(g)⇌2Cl(g) (fast)Cl(g)+ChCl3(g)=HCl+CCl3 (slow)Cl(g)+CCl3(g)=CCl4 (fast)
Definition
 Cl2(g)+CHCl3(g)=HCl+CCl4
Term
 Find Ea if:1) At 701k, rate constant= 2.57 L/mol•s2) At 895k, rc= 567 L/mol•s
Definition
 ln(k2/k1)=(Ea/r)(1/T1-1/T2)ln(567/2.57)=(Ea/8.314)(1/701-1/895)Ea= 14,500 kJ/mol
Term
 Write overall reaction:2NO(g)⇌N2O2(g) (fast)H2(g)+N2O2(g)=H2O(g)+N2O(g) (slow)N20(g)+H2(g)=N2(g)+H20(g) (fast)
Definition
 2NO+2H2=2H20+N2r= k3[H2][N2O2]k1[NO2]=k2[N2O2]2NO+2H2=2H2O+N2r= k3[H2][N2O2]=k3[H2](k1[NO]/k2)=(k3k1/k3)[H2][NO]r= k[H2][NO]^2
Term
 A certain reaction has the following general form: aA ==> bB At a particular temperature and [A]0 = 2.00 x 10^-2 M, concentration versus time data were collected for this reaction, and a plot of ln[A] versus time resulted in a straight line with a slope value of -2.97 x 10^-2 min^-1. a) Determine the rate law, the integrated rate law, and the value of the rate constant for this reaction. b) Calculate the half-life for this reaction. c) How much time is required for the concentration of A to decrease to 2.50 x 10^-3 M?
Definition
 a) k= [A]ln[A]= -0.0297t+ln[0.0200]k= -0.0297 m/sb) t 1/2= 0.693/0.0297=23.3 minutesc) ln(0.00250)= -0.0297t+0.0200t= 202.4 minutes
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