Chemical Kinetics. Copyright © Houghton Mifflin Company. All rights reserved. 15a–2 Close-up of a...

Chemical Kinetics

Copyright © Houghton Mifflin Company. All rights reserved. 15a–2

Close-up of a crashing wave.

Source: Getty Images




Figure 15.1: Starting with pure nitrogen dioxide at 300°C


Rate Law

instantaneous rate of reaction.

Rate = k(phenolphthalein)

the concentration of phenolphthalein in a solution that was initially 0.005 M in phenolphthalein and 0.61 M in OH- ion.


Examples of Rate Law

2 HI(g) H2(g) + I2(g)

CH3Br(aq) + OH-(aq) CH3OH(aq) + Br-(aq)

Rate = k(CH3Br)(OH-)

(CH3)3CBr(aq) + OH-(aq) (CH3)3COH(aq) + Br-

But Rate = k((CH3)3CBr)

Rate law is not related to stochiometry!


Decomposition of N2O5



Figure 15.2: Plot of the concentration of N2O5

Rate = k(N2O5)


Figure 15.3: A plot of In[N205] versus time.


Figure 15.4: Plot of [N2O5] versus time for the decomposition reaction of N2O5.


Rate = k(X)We then test this assumption by checking concentration versus time data

for the reaction to see whether they fit the first-order rate law.

ln (X) - ln (X)0 = - kt y = mx + b

ln (X) = -kt + ln (X)0


2nd Order Reaction

Rate = k(X)2




Solution containing BrO3-


Butadiene and its dimer


Figure 15.5: (a) A plot of ln[C4H6] versus t. (b) A plot of 1/[C4H6] versus t.


Figure 15.6: Plot of [A] versus t for a zero-order reaction


Figure 15.7: Decomposition reaction takes place on a platinum surface



Figure 15.8: Molecular representation of the elementary steps in the reaction of NO2 and CO.



Single Step Reaction

CH3Br(aq) + OH-(aq) CH3OH(aq) + Br-(aq)

Rate = k(CH3Br)(OH-)


Multiple Step Reaction

(CH3)3CBr(aq) + OH-(aq) (CH3)3COH(aq) + Br-(aq)

(CH3)3CBr (CH3)3C+ + Br- Slow step

(CH3)3C+ + H2O (CH3)3COH2

+ Fast step

(CH3)3COH2+ + OH- (CH3)3COH + H2O Fast step


General Rules for Rate Law

•The rate of any step in a reaction is directly proportional to the concentrations of the reagents consumed in that step.•The overall rate law for a reaction is determined by the sequence of steps, or the mechanism, by which the reactants are converted into the products of the reaction.•The overall rate law for a reaction is dominated by the rate law for the slowest step in the reaction.


The rate a which this colored solution enters the flask is determined by the size of the funnel stem, not how fast the solution is poured.

Source: American Color


Slow and Fast reactions shown as molecular models


Figure 15.10: A plot showing the exponential dependence of the rate constant on the absolute temperature


Figure 15.11: The change in potential energy as a function of reaction progress for the reaction


Figure 15.12: Plot showing the number of collisions with a particular energy


Figure 15.13: Several possible orientations for a collision between two BrNO molecules.


Figure 15.14: Plot of In(k) versus 1/T for the reaction


Figure 15.15: Energy plots for catalyzed and uncatalyzed pathways for a given reaction


Homogeneous Catalysis

H2O2(aq) + I-(aq) H2O(aq) + OI-(aq)

In the second step, the OI- ion is reduced to I- by H2O2.

OI-(aq) + H2O2(aq) H2O(aq) + O2(g) + I-(aq)

the first step in this reaction is the rate-limiting step,


Figure 15.16: Effect of a catalyst on the number of reaction-producing collisions.


Figure 15.17: Heterogeneous catalysis of the hydrogenation of ethylene.


Figure 15.18: The exhaust gases from an automobile engine are passed through a catalytic converter to

minimize environmental damage.


General structure of protein


Figure 15.19: Removal of the end amino acid from a protein by reaction with a molecule of water.


Figure 15.20: Structure of the enzymecarboxypeptidase-A, which contains 307 amino acids.


Figure 15.21: Protein-substrate interaction


Cutaway model of a catalytic converter used in automotive exhaust systems.

Source: Delphi Automotive Systems


Collect samples of extremophiles from


A micrograph of the extremophile Archaeoglobus fulgidis, and organis that lives in the hot sediments near

submarine hydrothermal vents.

Source: Photo Researchers, Inc.


Reaction coordinate


Reaction coordinate


Rate


Concentration of reactant


Time (s); Time (s); Time (s)


Laser spectroscopy

Source: California Institute of Technology


Figure 15.9: The STM images of the reaction of CO and O2

Source: University of California, Irvine

Date post:	20-Jan-2016
Category:	Documents
Upload:	penelope-rosa-lucas
View:	213 times
Download:	0 times

Chemical Kinetics. Copyright © Houghton Mifflin Company. All rights reserved. 15a–2 Close-up of a...

Documents