chemical equilibria why do we...
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![Page 1: Chemical Equilibria Why do we care?!!barbara.cm.utexas.edu/courses/ch302/files/CH302_020311.pdfPrinciples of Chemistry II © Vanden BoutFor the following reaction Δ RG = +740 kJ mol-1](https://reader034.vdocuments.us/reader034/viewer/2022042400/5f0f43a17e708231d4434c39/html5/thumbnails/1.jpg)
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Chemical Equilibria
Why do we care?!!
![Page 2: Chemical Equilibria Why do we care?!!barbara.cm.utexas.edu/courses/ch302/files/CH302_020311.pdfPrinciples of Chemistry II © Vanden BoutFor the following reaction Δ RG = +740 kJ mol-1](https://reader034.vdocuments.us/reader034/viewer/2022042400/5f0f43a17e708231d4434c39/html5/thumbnails/2.jpg)
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Put stuff in a beaker and what do you get?
We can use thermodynamics to predict the molecular concentrations at equilibrium
(very powerful!)
2H2O(g) 2H2(g) + O2(g)
ΔrG° = +113.4 kJ mol-1
![Page 3: Chemical Equilibria Why do we care?!!barbara.cm.utexas.edu/courses/ch302/files/CH302_020311.pdfPrinciples of Chemistry II © Vanden BoutFor the following reaction Δ RG = +740 kJ mol-1](https://reader034.vdocuments.us/reader034/viewer/2022042400/5f0f43a17e708231d4434c39/html5/thumbnails/3.jpg)
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What about the opposite reaction?
2H2(g) + O2(g) 2H2O(g)
ΔrG° = -113.4 kJ mol-1
![Page 4: Chemical Equilibria Why do we care?!!barbara.cm.utexas.edu/courses/ch302/files/CH302_020311.pdfPrinciples of Chemistry II © Vanden BoutFor the following reaction Δ RG = +740 kJ mol-1](https://reader034.vdocuments.us/reader034/viewer/2022042400/5f0f43a17e708231d4434c39/html5/thumbnails/4.jpg)
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Does everything go to equilibrium as predicted?
What happens if you mix H2 and O2 at 298K?
A. The explode and form water
B. They explode and form hydrogen peroxide (H2O2)
C. Nothing
![Page 5: Chemical Equilibria Why do we care?!!barbara.cm.utexas.edu/courses/ch302/files/CH302_020311.pdfPrinciples of Chemistry II © Vanden BoutFor the following reaction Δ RG = +740 kJ mol-1](https://reader034.vdocuments.us/reader034/viewer/2022042400/5f0f43a17e708231d4434c39/html5/thumbnails/5.jpg)
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Why didn’t I get to equilibrium?
Kinetics Other Reactions
![Page 6: Chemical Equilibria Why do we care?!!barbara.cm.utexas.edu/courses/ch302/files/CH302_020311.pdfPrinciples of Chemistry II © Vanden BoutFor the following reaction Δ RG = +740 kJ mol-1](https://reader034.vdocuments.us/reader034/viewer/2022042400/5f0f43a17e708231d4434c39/html5/thumbnails/6.jpg)
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Chemical Equilibria
Why do we care?!!
Things might not get to equilibriumbut they never move away from it
![Page 7: Chemical Equilibria Why do we care?!!barbara.cm.utexas.edu/courses/ch302/files/CH302_020311.pdfPrinciples of Chemistry II © Vanden BoutFor the following reaction Δ RG = +740 kJ mol-1](https://reader034.vdocuments.us/reader034/viewer/2022042400/5f0f43a17e708231d4434c39/html5/thumbnails/7.jpg)
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Why does K depend on ΔrG°?
A BimagineΔrG° = 0
G
Reaction
![Page 8: Chemical Equilibria Why do we care?!!barbara.cm.utexas.edu/courses/ch302/files/CH302_020311.pdfPrinciples of Chemistry II © Vanden BoutFor the following reaction Δ RG = +740 kJ mol-1](https://reader034.vdocuments.us/reader034/viewer/2022042400/5f0f43a17e708231d4434c39/html5/thumbnails/8.jpg)
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A B imagineΔrG° = 0
G
Reaction
![Page 9: Chemical Equilibria Why do we care?!!barbara.cm.utexas.edu/courses/ch302/files/CH302_020311.pdfPrinciples of Chemistry II © Vanden BoutFor the following reaction Δ RG = +740 kJ mol-1](https://reader034.vdocuments.us/reader034/viewer/2022042400/5f0f43a17e708231d4434c39/html5/thumbnails/9.jpg)
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A B imagineΔrG° > 0
G
Reaction
![Page 10: Chemical Equilibria Why do we care?!!barbara.cm.utexas.edu/courses/ch302/files/CH302_020311.pdfPrinciples of Chemistry II © Vanden BoutFor the following reaction Δ RG = +740 kJ mol-1](https://reader034.vdocuments.us/reader034/viewer/2022042400/5f0f43a17e708231d4434c39/html5/thumbnails/10.jpg)
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Figure Copyright Houghton Mifflin Company. All rights reserved
Equilibrium does not depend on starting conditions
Each equilibrium has different concentrations, but the same value for Kc
![Page 11: Chemical Equilibria Why do we care?!!barbara.cm.utexas.edu/courses/ch302/files/CH302_020311.pdfPrinciples of Chemistry II © Vanden BoutFor the following reaction Δ RG = +740 kJ mol-1](https://reader034.vdocuments.us/reader034/viewer/2022042400/5f0f43a17e708231d4434c39/html5/thumbnails/11.jpg)
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A convention to keep things straight
we’ll be doing a lot of aqueous problemsC denote concentrations initially
[ ] denote concentrations at equilibrium
3H2(g) + N2(g) 2NH3(g)Reaction
Initial
Change
Equilibrium
![Page 12: Chemical Equilibria Why do we care?!!barbara.cm.utexas.edu/courses/ch302/files/CH302_020311.pdfPrinciples of Chemistry II © Vanden BoutFor the following reaction Δ RG = +740 kJ mol-1](https://reader034.vdocuments.us/reader034/viewer/2022042400/5f0f43a17e708231d4434c39/html5/thumbnails/12.jpg)
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3H2(g) + N2(g) 2NH3(g)Reaction
Initial
Change
Equilibrium
Really Easy problemsAt equilibrium you find
[H2] = .1 M, [N2] = 0.2 M, and [NH3] = .2M
K =
![Page 13: Chemical Equilibria Why do we care?!!barbara.cm.utexas.edu/courses/ch302/files/CH302_020311.pdfPrinciples of Chemistry II © Vanden BoutFor the following reaction Δ RG = +740 kJ mol-1](https://reader034.vdocuments.us/reader034/viewer/2022042400/5f0f43a17e708231d4434c39/html5/thumbnails/13.jpg)
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3H2(g) + N2(g) 2NH3(g)Reaction
Initial
Change
Equilibrium
Fairly Easy problem Given K = 200 and [H2] = .2 M, [N2] = 0.4 M, and CNH3 = .1M
fill in the rest
![Page 14: Chemical Equilibria Why do we care?!!barbara.cm.utexas.edu/courses/ch302/files/CH302_020311.pdfPrinciples of Chemistry II © Vanden BoutFor the following reaction Δ RG = +740 kJ mol-1](https://reader034.vdocuments.us/reader034/viewer/2022042400/5f0f43a17e708231d4434c39/html5/thumbnails/14.jpg)
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3H2(g) + N2(g) 2NH3(g)Reaction
Initial
Change
Equilibrium
Typical problem
Given K = 200 and CH2 = .2 M, N2 = 0.2 M what are the
concentrations at equilibrium
![Page 15: Chemical Equilibria Why do we care?!!barbara.cm.utexas.edu/courses/ch302/files/CH302_020311.pdfPrinciples of Chemistry II © Vanden BoutFor the following reaction Δ RG = +740 kJ mol-1](https://reader034.vdocuments.us/reader034/viewer/2022042400/5f0f43a17e708231d4434c39/html5/thumbnails/15.jpg)
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3H2(g) + N2(g) 2NH3(g)Reaction
Initial
Change
Equilibrium
.2 .2 0
-3x -x +2x
.2-3x .2-x +2x
![Page 16: Chemical Equilibria Why do we care?!!barbara.cm.utexas.edu/courses/ch302/files/CH302_020311.pdfPrinciples of Chemistry II © Vanden BoutFor the following reaction Δ RG = +740 kJ mol-1](https://reader034.vdocuments.us/reader034/viewer/2022042400/5f0f43a17e708231d4434c39/html5/thumbnails/16.jpg)
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I thought you said we need to use Kp for gases
and Kc for solutions?
![Page 17: Chemical Equilibria Why do we care?!!barbara.cm.utexas.edu/courses/ch302/files/CH302_020311.pdfPrinciples of Chemistry II © Vanden BoutFor the following reaction Δ RG = +740 kJ mol-1](https://reader034.vdocuments.us/reader034/viewer/2022042400/5f0f43a17e708231d4434c39/html5/thumbnails/17.jpg)
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Relating Kp and Kc
2NO2(g) N2O4(g)
Kc = Kp =
PN2O4 =
![Page 18: Chemical Equilibria Why do we care?!!barbara.cm.utexas.edu/courses/ch302/files/CH302_020311.pdfPrinciples of Chemistry II © Vanden BoutFor the following reaction Δ RG = +740 kJ mol-1](https://reader034.vdocuments.us/reader034/viewer/2022042400/5f0f43a17e708231d4434c39/html5/thumbnails/18.jpg)
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Relating Kp and Kc
2NO2(g) N2O4(g)
Kp =PN2O4
PNO22
=[N2O4]RT
[NO2]2(RT)2 =
In general KP = Kc(RT)Δn
Δn is the change in the number of moles of gas
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Time out for activities
That is what we are actually putting into the equilibrium constant
Gas
ai =
Compoundin solution
ai =
Free Energy Changes with P
Free Energy Changes with Concentration
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What about the activity of a pure liquid or solid?
ai =
The pure compound is the reference state!
Pure solids and liquids “don’t show up”in the equilibrium constant
(they are there. they are just always = 1)
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What is the equilibrium constant for this reaction?
H2O(l) H2O(g)
K =
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Equilibria with more than one phaseare called Heterogeneous Equilibria
CaCO3(s) CaO(s) + CO2(g)
K=
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For the following reaction ΔRG° = +740 kJ mol-1 at 298KIn air will I form any solid iron?
Fe2O3(s) 2Fe(s) + (3/2)O2(g)
A. all the iron oxide will convert to iron
B. about half of the iron oxide will convert to iron
C. a very small amount of the iron oxide will convert to iron
D. not a single atom of iron will form
![Page 24: Chemical Equilibria Why do we care?!!barbara.cm.utexas.edu/courses/ch302/files/CH302_020311.pdfPrinciples of Chemistry II © Vanden BoutFor the following reaction Δ RG = +740 kJ mol-1](https://reader034.vdocuments.us/reader034/viewer/2022042400/5f0f43a17e708231d4434c39/html5/thumbnails/24.jpg)
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For the following reaction ΔRG° = +740 kJ mol-1 at 298KIn air will I form any solid iron?
Fe2O3(s) 2Fe(s) + (3/2)O2(g)
What is Q?
K= exp[-740,000/(8.314)(298)] = 2 x 10-130
![Page 25: Chemical Equilibria Why do we care?!!barbara.cm.utexas.edu/courses/ch302/files/CH302_020311.pdfPrinciples of Chemistry II © Vanden BoutFor the following reaction Δ RG = +740 kJ mol-1](https://reader034.vdocuments.us/reader034/viewer/2022042400/5f0f43a17e708231d4434c39/html5/thumbnails/25.jpg)
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What is equilibrium good for?
Drug + Protein Drug-Protein Complex
Fendrick et al. Osteopathic Medicine and Primary Care 2008 2:2 doi:10.1186/1750-4732-2-2
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Drug BindingHow “strongly” should it bind to work?
Drug + Protein Drug-Protein Complex
K =
Do an experiment Measure K
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For ibuprofin binding to the COX channel K ~ 108
Drug + Protein Drug-Protein Complex
If we want 100x more complexed protein than free proteinwhat concentration of drug do we need?
A. 10-8 M
B. 10-6 M
C. 10-4 M
D. 10-2 M
K = [complex]
[drug][protein]
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How much is that?
Person is 50 kg = 50 L of water
MW of ibuprofin is ~200 g mol-1
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For the following reaction what is the change value for H2O?
2C2H6(g) + 7O2(g) 4CO2(g) + 6H2O(g)
R C2H6 O2 CO2 H2O
I 1.0 1.4 1.8 0
C -2x ? ? ?
A. -2x
B. +2x
C. +3x
D. +6x
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For the following reaction what is the equilibrium value for CO2?
2C2H6(g) + 7O2(g) 4CO2(g) + 6H2O(g)
R C2H6 O2 CO2 H2O
I 1.0 1.4 1.8 0
C -2x ? ? ?
A. 1.8 - 2x
B. 1.8 + 2x
C. 1.8 + 4x
D. 1.0 + 6x