EquilibriumEquilibriumChap. 18Chap. 18Chap. 18Chap. 18

I.I. Introduction: Introduction: did you know that. . .did you know that. . .

I.I. Introduction: Introduction:

A.A. Reactions don’t always Reactions don’t always completely use up reactantscompletely use up reactants

did you know that. . .did you know that. . .

A + 2B C

Consider a reaction between 50 molecules of A and 100 molecules of B. What’s left at the end?

I.I. Introduction: Introduction:

A.A. Reactions don’t always Reactions don’t always completely use up reactantscompletely use up reactants

B.B. Reactions are reversibleReactions are reversible

did you know that. . .did you know that. . .

Can you ‘un-rust’ or ‘un-combust’?

I.I. Introduction: Introduction:

A.A. Reactions don’t always Reactions don’t always completely use up reactantscompletely use up reactants

B.B. Reactions are reversibleReactions are reversible

C.C. Arrows represent the Arrows represent the forwardforward

did you know that. . .did you know that. . .

A + 2B C

I.I. Introduction: Introduction:

A.A. Reactions don’t always Reactions don’t always completely use up reactantscompletely use up reactants

B.B. Reactions are reversibleReactions are reversible

C.C. Arrows represent the Arrows represent the forwardforward and and reversereverse reactions reactions

did you know that. . .did you know that. . .

A + 2B C

I.I. Introduction: Introduction:

A.A. Reactions don’t always Reactions don’t always completely use up reactantscompletely use up reactants

B.B. Reactions are reversibleReactions are reversible

C.C. Arrows represent the forward Arrows represent the forward and reverse reactionsand reverse reactions

D.D. Reaction rates depend on the Reaction rates depend on the concentration of reactantsconcentration of reactants

did you know that. . .did you know that. . .

I.I. Introduction: Introduction:

A.A. Reactions don’t always Reactions don’t always completely use up reactantscompletely use up reactants

B.B. Reactions are reversibleReactions are reversible

C.C. Arrows represent the forward Arrows represent the forward and reverse reactionsand reverse reactions

D.D. Reaction rates depend on the Reaction rates depend on the concentration of reactantsconcentration of reactants

E.E. The symbols, The symbols, [ ][ ] mean mean concentration (molarity)concentration (molarity)

did you know that. . .did you know that. . .

II.II. An exampleAn example

II.II. An exampleAn exampleNN22 + 3H + 3H22 2NH 2NH33

Imagine putting equal amounts of HImagine putting equal amounts of H22 and Nand N22 in an empty container. in an empty container.

II.II. An exampleAn example

A.A. Initially the rate of the reverse Initially the rate of the reverse reaction is reaction is because… because…

NN22 + 3H + 3H22 2NH 2NH33

Imagine putting equal amounts of HImagine putting equal amounts of H22 and Nand N22 in an empty container. in an empty container.

II.II. An exampleAn example

A.A. Initially the rate of the reverse Initially the rate of the reverse reaction is reaction is zerozero because… because…

NN22 + 3H + 3H22 2NH 2NH33

Imagine putting equal amounts of HImagine putting equal amounts of H22 and Nand N22 in an empty container. in an empty container.

II.II. An exampleAn example

A.A. Initially the rate of the reverse Initially the rate of the reverse reaction is reaction is zerozero because… because…

B.B. Initially the rate of the forward Initially the rate of the forward reaction is relatively ___reaction is relatively ___ because…because…

NN22 + 3H + 3H22 2NH 2NH33

Imagine putting equal amounts of HImagine putting equal amounts of H22 and Nand N22 in an empty container. in an empty container.

II.II. An exampleAn example

A.A. Initially the rate of the reverse Initially the rate of the reverse reaction is reaction is zerozero because… because…

B.B. Initially the rate of the forward Initially the rate of the forward reaction is relatively reaction is relatively fastfast because…because…

NN22 + 3H + 3H22 2NH 2NH33

Imagine putting equal amounts of HImagine putting equal amounts of H22 and Nand N22 in an empty container. in an empty container.

II.II. An exampleAn example

C.C. Over time, the rate of the Over time, the rate of the reverse reaction reverse reaction _______ _______ and the rate of the and the rate of the forward reaction forward reaction ..

NN22 + 3H + 3H22 2NH 2NH33

Imagine putting equal amounts of HImagine putting equal amounts of H22 and Nand N22 in an empty container. in an empty container.

II.II. An exampleAn example

C.C. Over time, the rate of the Over time, the rate of the reverse reaction reverse reaction increasesincreases and the rate of the forward and the rate of the forward reaction reaction decreasesdecreases..

D.D. Eventually the two rates are Eventually the two rates are ____ ____..

NN22 + 3H + 3H22 2NH 2NH33

Imagine putting equal amounts of HImagine putting equal amounts of H22 and Nand N22 in an empty container. in an empty container.

II.II. An exampleAn example

C.C. Over time, the rate of the Over time, the rate of the reverse reaction reverse reaction increasesincreases and the rate of the forward and the rate of the forward reaction reaction decreasesdecreases..

D.D. Eventually the two rates are Eventually the two rates are equalequal..

NN22 + 3H + 3H22 2NH 2NH33

Imagine putting equal amounts of HImagine putting equal amounts of H22 and Nand N22 in an empty container. in an empty container.

III.III. Describing EquilibriumDescribing Equilibrium

III.III. Describing EquilibriumDescribing Equilibrium

A.A. A situation in which the A situation in which the forward and reverse forward and reverse reaction rates reaction rates ..

III.III. Describing EquilibriumDescribing Equilibrium

A.A. A situation in which the A situation in which the forward and reverse forward and reverse reaction rates reaction rates areare equalequal..

B.B. A situation where the A situation where the amounts of reactants/ amounts of reactants/ products products ..

III.III. Describing EquilibriumDescribing Equilibrium

A.A. A situation in which the A situation in which the forward and reverse forward and reverse reaction rates reaction rates areare equalequal..

B.B. A situation where the A situation where the amounts of reactants/ amounts of reactants/ products products remainremain constantconstant..

III.III. Describing EquilibriumDescribing Equilibrium

C.C. Equilibrium is dynamic.Equilibrium is dynamic.

Although the amount of products and reactants remains constant the reaction doesn’t ‘stop’ at equilibrium

IV.IV. Quantifying EquilibriumQuantifying Equilibrium

IV.IV. Quantifying EquilibriumQuantifying Equilibrium

A.A. At equilibrium the ratio of At equilibrium the ratio of product concentrations to product concentrations to reactant concentrations is a reactant concentrations is a constantconstant

IV.IV. Quantifying EquilibriumQuantifying Equilibrium

A.A. At equilibrium the ratio of At equilibrium the ratio of product concentrations to product concentrations to reactant concentrations is a reactant concentrations is a constantconstant

B.B. The symbol for this constant The symbol for this constant is: is: KKeqeq

IV.IV. Quantifying EquilibriumQuantifying Equilibrium

A.A. At equilibrium the ratio of At equilibrium the ratio of product concentrations to product concentrations to reactant concentrations is a reactant concentrations is a constantconstant

B.B. The symbol for this constant The symbol for this constant is: is: KKeqeq

C.C. The The equilibriumequilibrium expressionexpression::

KKeqeq = = [products][products]

[products][products]

IV.IV. Quantifying EquilibriumQuantifying Equilibrium

D.D. Equations with coefficientsEquations with coefficients

aaA + A + bbB B ccC + C + ddDDequation:

expression:

IV.IV. Quantifying EquilibriumQuantifying Equilibrium

D.D. Equations with coefficientsEquations with coefficients

KKeqeq = = [C][C]c c xx [D] [D]dd

[A][A]a a xx [B] [B]bb

aaA + A + bbB B ccC + C + ddDDequation:

expression:

IV.IV. Quantifying EquilibriumQuantifying Equilibrium

D.D. Equations with coefficientsEquations with coefficients

E.E. Significance of Significance of KKeqeq

IV.IV. Quantifying EquilibriumQuantifying Equilibrium

D.D. Equations with coefficientsEquations with coefficients

E.E. Significance of Significance of KKeqeq

KKeqeq = = expression:

1.1. A large A large KKeqeq

IV.IV. Quantifying EquilibriumQuantifying Equilibrium

D.D. Equations with coefficientsEquations with coefficients

E.E. Significance of Significance of KKeqeq

KKeqeq = = [Products][Products]

[Reactants][Reactants]

expression:

1.1. A large A large KKeqeq

IV.IV. Quantifying EquilibriumQuantifying Equilibrium

D.D. Equations with coefficientsEquations with coefficients

E.E. Significance of Significance of KKeqeq

KKeqeq = = expression:

1.1. A large A large KKeqeq

2.2. A small A small KKeqeq

IV.IV. Quantifying EquilibriumQuantifying Equilibrium

D.D. Equations with coefficientsEquations with coefficients

E.E. Significance of Significance of KKeqeq

KKeqeq = = expression:

1.1. A large A large KKeqeq

2.2. A small A small KKeqeq

[Products][Products]

[Reactants][Reactants]

V.V. Types of EquilibriaTypes of Equilibria

V.V. Types of EquilibriaTypes of Equilibria

A.A. HomogeneousHomogeneous

All substances in the same physical state

2NO2NO22 (g) N (g) N22OO44 (g) (g)

V.V. Types of EquilibriaTypes of Equilibria

A.A. HomogeneousHomogeneous

B.B. HeterogeneousHeterogeneous

Substances not all in the same physical state

C (s) + HC (s) + H22O (g) CO (g) + HO (g) CO (g) + H22 (g) (g)

VI.VI. Writing Equilibria Writing Equilibria ExpressionsExpressions

VI.VI. Writing Equilibria Writing Equilibria ExpressionsExpressions

A.A. KKeqeq = =[products][products]xx

[reactants][reactants]yy

VI.VI. Writing Equilibria Writing Equilibria ExpressionsExpressions

A.A. KKeqeq = =

B.B. Use balanced equation to Use balanced equation to decide on exponents.decide on exponents.

[products][products]xx

[reactants][reactants]yy

VI.VI. Writing Equilibria Writing Equilibria ExpressionsExpressions

A.A. KKeqeq = =

B.B. Use balanced equation to Use balanced equation to decide on exponents.decide on exponents.

C.C. Don’t include (s) or (Don’t include (s) or (ll) ) physical states in expression. physical states in expression.

[products][products]xx

[reactants][reactants]yy

Self Check – Ex. 1Self Check – Ex. 1

Write the Write the equilibrium equilibrium expressionexpression for the reaction for the reaction below.below.

NH3 (g) + HCl (g) NH4Cl (s)

Self Check – Ex. 2Self Check – Ex. 2

Write the Write the equilibrium equilibrium expressionexpression for the reaction for the reaction below.below.

2H2S (g) + SO2 (g) 3S (l) + 2H2O (g)

VII.VII. Calculating Equilibria Calculating Equilibria Constant ValuesConstant Values

VII.VII. Calculating Equilibria Calculating Equilibria Constant ValuesConstant Values

A.A. Write equilibrium expressionWrite equilibrium expression

VII.VII. Calculating Equilibria Calculating Equilibria Constant ValuesConstant Values

A.A. Write equilibrium expressionWrite equilibrium expression

B.B. Plug in equilibrium Plug in equilibrium concentrationsconcentrations

* a set of equilibrium concentrations is called an equilibrium position

VIII.VIII. Determining if reaction Determining if reaction is at equilibriumis at equilibrium

VIII.VIII. Determining if reaction Determining if reaction is at equilibriumis at equilibrium

A.A. Write equilibrium expression Write equilibrium expression using Qusing Q

Q is the reaction quotient, a value that is compared to Keq

VIII.VIII. Determining if reaction Determining if reaction is at equilibriumis at equilibrium

A.A. Write equilibrium expression Write equilibrium expression using Qusing Q

B.B. Plug in concentrationsPlug in concentrations

VIII.VIII. Determining if reaction Determining if reaction is at equilibriumis at equilibrium

A.A. Write equilibrium expression Write equilibrium expression using Qusing Q

B.B. Plug in concentrationsPlug in concentrations1.1. If Q > If Q > KKeqeq then reaction must then reaction must

‘go to the left’‘go to the left’

VIII.VIII. Determining if reaction Determining if reaction is at equilibriumis at equilibrium

A.A. Write equilibrium expression Write equilibrium expression using Qusing Q

B.B. Plug in concentrationsPlug in concentrations1.1. If Q > If Q > KKeqeq then reaction must then reaction must

‘go to the left’‘go to the left’

2.2. If Q < If Q < KKeqeq then reaction must then reaction must ‘go to the right’‘go to the right’

VIII.VIII. Determining if reaction Determining if reaction is at equilibriumis at equilibrium

A.A. Write equilibrium expression Write equilibrium expression using Qusing Q

B.B. Plug in concentrationsPlug in concentrations1.1. If Q > If Q > KKeqeq then reaction must then reaction must

‘go to the left’‘go to the left’

2.2. If Q < If Q < KKeqeq then reaction must then reaction must ‘go to the right’‘go to the right’

3.3. If Q = If Q = KKeqeq it’s at equilibrium it’s at equilibrium

Self Check – Ex. 3Self Check – Ex. 3Is this reaction at equilibrium?Is this reaction at equilibrium?

N2 (g) + 3H2 (g) 2NH3 (g) Keq = 0.105

[N2] = 0.0020 M

[H2] = 0.10 M

[NH3] = 0.15 M

Self Check – Ex. 4Self Check – Ex. 4Is the following reaction at Is the following reaction at equilibrium?equilibrium?

2CO (g) + O2 (g) CO2 (g) Keq = 0.0021

[CO] = 0.28 M

[O2] = 0.42 M

[CO2] = 1.21 M

IX.IX. Shifting Equilibrium: Shifting Equilibrium: LeChatelier’s PrincipleLeChatelier’s Principle

LeChatelier’s PrincipleLeChatelier’s Principle

When a change is imposed on a system at equilibrium, the equilibrium position shifts to minimize that change

When a change is imposed on a system at equilibrium, the equilibrium position shifts to minimize that change

IX.IX. Shifting Equilibrium: Shifting Equilibrium: LeChatelier’s PrincipleLeChatelier’s Principle

A.A. Changing ConcentrationsChanging Concentrations

Only affects equilibrium for gases and aqueous substances.

IX.IX. Shifting Equilibrium: Shifting Equilibrium: LeChatelier’s PrincipleLeChatelier’s Principle

A.A. Changing ConcentrationsChanging Concentrations

B.B. Changing VolumeChanging Volume

When volume decreases equilibrium shifts to the side with the fewest gas particles.

IX.IX. Shifting Equilibrium: Shifting Equilibrium: LeChatelier’s PrincipleLeChatelier’s Principle

A.A. Changing ConcentrationsChanging Concentrations

B.B. Changing VolumeChanging Volume

C.C. Changing TemperatureChanging Temperature

Decreasing temperature shifts equilibrium toward side with ‘heat’ written on it.

IX.IX. Shifting Equilibrium: Shifting Equilibrium: LeChatelier’s PrincipleLeChatelier’s Principle

A.A. Changing ConcentrationsChanging Concentrations

B.B. Changing VolumeChanging Volume

C.C. Changing TemperatureChanging Temperature1.1. Endothermic reactions: heat is Endothermic reactions: heat is

on the on the left sideleft side

IX.IX. Shifting Equilibrium: Shifting Equilibrium: LeChatelier’s PrincipleLeChatelier’s Principle

A.A. Changing ConcentrationsChanging Concentrations

B.B. Changing VolumeChanging Volume

C.C. Changing TemperatureChanging Temperature1.1. Endothermic reactions: heat is Endothermic reactions: heat is

on the on the left sideleft side

2.2. Exothermic reactions: heat is Exothermic reactions: heat is on the on the right sideright side

Self Check – Ex. 5Self Check – Ex. 5How do these changes shift equilibrium How do these changes shift equilibrium for this exothermic reaction?for this exothermic reaction?

CO (g) + H2 (g) H2O (g) + C (s)

Self Check – Ex. 5Self Check – Ex. 5How do these changes shift equilibrium How do these changes shift equilibrium for this exothermic reaction?for this exothermic reaction?

CO (g) + H2 (g) H2O (g) + C (s)

• [CO] is increased

Self Check – Ex. 5Self Check – Ex. 5How do these changes shift equilibrium How do these changes shift equilibrium for this exothermic reaction?for this exothermic reaction?

CO (g) + H2 (g) H2O (g) + C (s)

• [CO] is increased

• Water vapor is added

Self Check – Ex. 5Self Check – Ex. 5How do these changes shift equilibrium How do these changes shift equilibrium for this exothermic reaction?for this exothermic reaction?

CO (g) + H2 (g) H2O (g) + C (s)

• [CO] is increased

• Water vapor is added

• Carbon is added

Self Check – Ex. 5Self Check – Ex. 5How do these changes shift equilibrium How do these changes shift equilibrium for this exothermic reaction?for this exothermic reaction?

CO (g) + H2 (g) H2O (g) + C (s)

• [CO] is increased

• Water vapor is added

• Carbon is added

• Volume is decreased

Self Check – Ex. 5Self Check – Ex. 5How do these changes shift equilibrium How do these changes shift equilibrium for this exothermic reaction?for this exothermic reaction?

CO (g) + H2 (g) H2O (g) + C (s)

• [CO] is increased

• Water vapor is added

• Carbon is added

• Volume is decreased

• Temperature is increased

IX.IX. Shifting Equilibrium: Shifting Equilibrium: LeChatelier’s PrincipleLeChatelier’s Principle

A.A. Changing ConcentrationsChanging Concentrations

B.B. Changing VolumeChanging Volume

C.C. Changing TemperatureChanging Temperature

D.D. Haber’s ProcessHaber’s Process

X.X. Solubility EquilibriaSolubility Equilibria

X.X. Solubility EquilibriaSolubility EquilibriaA.A. TermsTerms

X.X. Solubility EquilibriaSolubility EquilibriaA.A. TermsTerms

1.1. DissolutionDissolution

Process in which an ionic solid dissolves into a liquid, separating into its ions, and ‘entering the solution’.

X.X. Solubility EquilibriaSolubility EquilibriaA.A. TermsTerms

1.1. DissolutionDissolution

2.2. PrecipitationPrecipitation

Process in which dissolved ions rejoin to form an ionic compound and they ‘leave the solution’.

X.X. Solubility EquilibriaSolubility EquilibriaA.A. TermsTerms

1.1. DissolutionDissolution

2.2. PrecipitationPrecipitation

3.3. SolubilitySolubility

The amount of solute that dissolves in a given volume of solvent.

Self Check – Ex. 6Self Check – Ex. 6

If a substance had a solubility If a substance had a solubility of of zerozero we’d say that substance we’d say that substance is is in water. in water.

Self Check – Ex. 6Self Check – Ex. 6

If a substance had a solubility If a substance had a solubility of of zerozero we’d say that substance we’d say that substance is is insolubleinsoluble in water. in water.

X.X. Solubility EquilibriaSolubility EquilibriaA.A. TermsTerms

B.B. Solubility EquilibriumSolubility Equilibrium

Conditions in which the rate of dissolution equals the rate of precipitation.

X.X. Solubility EquilibriaSolubility EquilibriaA.A. TermsTerms

B.B. Solubility EquilibriumSolubility Equilibrium

C.C. The Solubility Product The Solubility Product constant (constant (KKspsp) Expression) Expression

Remember to only include aqueous substances.

CaCO3 (s) Ca2+ (aq) + CO32- (aq)

Self Check – Ex. 7Self Check – Ex. 7

Write the solubility product Write the solubility product expression for calcium expression for calcium hydroxide, Ca(OH)hydroxide, Ca(OH)22..

*hint – first write the solubility equation.*hint – first write the solubility equation.

X.X. Solubility EquilibriaSolubility EquilibriaD.D. CalculationsCalculations

X.X. Solubility EquilibriaSolubility EquilibriaD.D. CalculationsCalculations

1.1. Finding Finding KKspsp

Self Check – Ex. 8Self Check – Ex. 8

When Mg(OH)When Mg(OH)22 reaches reaches

equilibrium the concentration of equilibrium the concentration of MgMg2+2+ ions is 1.1 ions is 1.1 x x 1010-4-4 mol/L. mol/L. Determine Determine KKspsp for this reaction.for this reaction.

X.X. Solubility EquilibriaSolubility EquilibriaD.D. CalculationsCalculations

1.1. Finding Finding KKspsp

2.2. Finding solubilityFinding solubility

Find the moles/liter of solid that dissolves.

Self Check – Ex. 9Self Check – Ex. 9

Using the following table find the Using the following table find the solubility of PbFsolubility of PbF22..

X.X. Solubility EquilibriaSolubility EquilibriaD.D. CalculationsCalculations

1.1. Finding Finding KKspsp

2.2. Finding solubilityFinding solubility

3.3. Equilibrium concentrationsEquilibrium concentrations

Self Check – Ex. 10Self Check – Ex. 10

What are the equilibrium What are the equilibrium concentrations of Alconcentrations of Al3+3+ and OH and OH-- in in a solution containing the slightly a solution containing the slightly soluble Al(OH)soluble Al(OH)33??

X.X. Solubility EquilibriaSolubility EquilibriaD.D. CalculationsCalculations

E.E. Predicting precipitatesPredicting precipitates

If Q ≥ Ksp, then a precipitate forms.

the end