Chemical Equilibrium Chapter 18 Modern Chemistry

Chapter 18 Section 2 Shifting Equilibrium p. 598-604

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ChemicalEquilibriumChapter 18

Modern ChemistrySections 1 & 2

The Nature of Chemical EquilibriumShifting Equilibrium


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Shifting Equilibrium

Section 18.2


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Seesaws and Equilibrium


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LeChatelier’s PrincipleA play in one act.


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TEACHER: “Let’s put stress on the equilibrium!”STUDENTS: “How?” (puzzled)

TEACHER: “Change the T, P, or concentration.”

LECHATELIER: “A new equilibrium will be attained.”

STUDENTS: “How?” (amazed)

TEACHER: “One of the reactions will go faster,

for a while, to relieve the stress.”

STUDENTS: “I understand.” (with confidence)


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The End.


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LeC

hate

lier’

s P

rin

cip

le


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If a system at equilibrium is subjected to a stress, the equilibrium is shifted in the direction that tends to relieve the stress…and a new equilibrium is achieved.

LeChatelier’s Principle


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Changing the concentration Adding a reactant or product Removing a reactant or product

Changing the temperature. Changing the pressure

How is a system “stressed”?


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Affects only eq. with gases Increasing the pressure favors the side

with the fewest particles Leading to a decrease in pressure

Decreasing the pressure favors the side with the most particles Leading to an increase in pressure

If particle are equal, pressure has no effect.

Increasing pressure by adding a gas that is not a reactant or a product cannot affect the eq.

Changes in Pressure


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2NO2 (g) N2O4 (g) + Energy

O2 (g) + 2SO2 (g) + Energy 2SO3 (g)

N2 (g) + 3 H2 (g) 2NH3 (g) + Energy

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

O2 (g) + N2 (g) 2NO2 (g) Keq = 4.5 x 10-31 at 25 ° C Keq = 6.7 x 10-10 at 627 °C

Balanced Equation


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Central Metal Surrounded by

ligands Examples of

ligands H2O NH3

CN1-

Cl1-

Complex Ions


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Increase the concentration of reactants the forward reaction is favored

Increase the concentration of products the reverse reaction is favored

Up, Up and AwayUp, Up and Away

Take Away TowardsTake Away Towards

Changes in Concentration


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[Cu(H2O)4 ] 2+ + 4Cl1- [CuCl4]2- + 4H2O

Complex Cu Ion System

1.Increase Cl1-

2.Shift is forward

3.Products increase, reactants decrease

4.The Keq is the same – before and after

AWAYUP, UP


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[Cu(H2O)4 ] 2+ + 4Cl1- [CuCl4]2- + 4H2O

Complex Cu Ion System

1.Increase H2O

2.Shift is reverse

3.Reactants increase, products decrease

4.The Keq is the same – before & after

AWAY UP, UP


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[CoCl4]2- + 6H2O [Co(H2O)6]2+ + 4Cl-

Complex Co Ion System

1.Decrease H2O

2.Shift is reverse

3.Reactants increase, products decrease

4.The Keq is the same – before & after

TOWARDS

TAKE AWAY


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N2 (g) + 3 H2 (g) 2NH3 (g) + Energy



Balanced Equation


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2NO2 (g) N2O4 (g) + Energy In a reversible reaction one direction is

exothermic and the other direction is endothermic.

In the reaction above which direction is exothermic?

forward endothermic?

reverse

Changes in Temperature


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2NO2 (g) N2O4 (g) + Energy Increasing the energy favors the endothermic

reaction Decreasing the energy favors the exothermic

reaction Keq is dependant on temperature A change in temp, changes the Keq.



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Equilibrium Constants Table


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NO2 N2O4 System


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NO2 N2O4 System

1.Increase Energy (temperature)

2.Shift is reverse

3.Products decrease, reactants increase

4.The Keq is decreasing

AWAYUP, UP


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NO2 N2O4 System

1.Decrease Energy (temperature)

2.Shift is forward

3.Products increase, reactants decrease

4.The Keq is increasing

TOWARDS TAKE AWAY


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engine runningstoring energythat is taken in

engine not runningusing energy that isgiven off

Pb(s) + PbO(s) + 2H2SO4(aq) 2PbSO4(s) + 2H2O(l) + E


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N2 (g) + 3 H2 (g) 2NH3 (g) + Energy



Balanced Equation


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Eff

ect

of

T,

P &

Con

c


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CO2(g) CO2(aq) H2CO3(aq) H+ + HCO3- (aq)

H+ + CO3-2

(aq) + Ca2+ CaCO3(s)

Chickens Lose Equilibrium

EGGSHELL

CHICKENBREATH


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If a product leaves the system the reaction will not reverse. It will go to completion.

Formation of a gas. H2CO3 (aq) H2O(l) + CO2(g)

Formation of a precipitate. Na+

(aq)+Cl−(aq)+Ag+(aq)+NO3−

(aq) Na+(aq)+NO3−

(aq)+AgCl (s)

Reactions that go to completion


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Com

mon

Ion

Eff

ect


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The addition of HCl caused the NaCl to increase and precipitate out of solution.

Common-ion Effect - the addition of an ion common to two solutes brings about precipitation or reduced ionization.

Common Ion Effect

HCl (g) H+(aq) + Cl−(aq)

AWAYUP, UP

NaCl (s) Na+(aq) + Cl−(aq)


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Adding acetate ion from the dissociation of sodium acetate causes a reverse shift.

Ionization is reduced. [H3O] is reduced.

Common Ion EffectNaC2H3O2 Na+ + C2H3O2

-

AWAY UP, UPHC2H3O2 (aq)H2O(l) H3O

(aq)C2H3O2−

(aq)


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Ch 18 Sec 2 Homework

LeChatelier’s Principle Worksheet

Chemical Equilibrium Chapter 18 Modern Chemistry

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