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Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles

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Page 1: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

Atkins & de Paula: Elements of Physical Chemistry:

5e

Atkins & de Paula: Elements of Physical Chemistry:

5e

Chapter 7: Chemical Equilibrium: The

Principles

Chapter 7: Chemical Equilibrium: The

Principles

Page 2: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

End of chapter 7 assignmentsEnd of chapter 7 assignments

Discussion questions:• 2

Exercises:• 1, 2, 3, 4, 5, 6, 7, 10, 11, 15,

18

Use Excel if data needs to be graphed

Discussion questions:• 2

Exercises:• 1, 2, 3, 4, 5, 6, 7, 10, 11, 15,

18

Use Excel if data needs to be graphed

Page 3: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

Homework AssignmentHomework Assignment

• How many of you have already read all of chapter 7 in the textbook?

• In the future, read the entire chapter in the textbook before we begin discussing it in class

• How many of you have already read all of chapter 7 in the textbook?

• In the future, read the entire chapter in the textbook before we begin discussing it in class

Page 4: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

Homework AssignmentHomework Assignment

• Connect to the publisher’s website and access all “Living Graphs”

• http://bcs.whfreeman.com/elements4e/

• Change the parameters and observe the effects on the graph

• Sarah: these “Living Graphs” are not really living; this is just a hokey name!

• Connect to the publisher’s website and access all “Living Graphs”

• http://bcs.whfreeman.com/elements4e/

• Change the parameters and observe the effects on the graph

• Sarah: these “Living Graphs” are not really living; this is just a hokey name!

Page 5: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

Homework AssignmentsHomework Assignments

• Read Chapter 7.• Work through all of the

“Illustration” boxes and the “Example” boxes and the “Self-test” boxes in Chapter 7.

• Work the assigned end-of-chapter exercises by the due date

• Read Chapter 7.• Work through all of the

“Illustration” boxes and the “Example” boxes and the “Self-test” boxes in Chapter 7.

• Work the assigned end-of-chapter exercises by the due date

Page 6: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

Principles of chemical equilibrium

Principles of chemical equilibrium

Central Concepts:• Thermodynamics can predict

whether a rxn has a tendency to form products, but it says nothing about the rate

• At constant T and P, a rxn mixture tends to adjust its composition until its Gibbs energy is at a minimum

Central Concepts:• Thermodynamics can predict

whether a rxn has a tendency to form products, but it says nothing about the rate

• At constant T and P, a rxn mixture tends to adjust its composition until its Gibbs energy is at a minimum

Page 7: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

Gibbs Energy vs Progress of Rxn

Gibbs Energy vs Progress of Rxn

• Fig 7.1 (158)• (a) does not go• (b) equilibrium with

amount of reactants ~amount of products

• (c) goes to completion

• Fig 7.1 (158)• (a) does not go• (b) equilibrium with

amount of reactants ~amount of products

• (c) goes to completion

Page 8: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

Example RxnsExample Rxns

• G6P(aq) F6P(aq)

• N2(g) + 3 H2(g) 2 NH3(g)

• Reactions are of this form: aA + bB cC + dD

• If n is small enough, then,G = (F6P x n) – (G6P x n) --now divide by n

rG = G/n = F6P – G6P

• G6P(aq) F6P(aq)

• N2(g) + 3 H2(g) 2 NH3(g)

• Reactions are of this form: aA + bB cC + dD

• If n is small enough, then,G = (F6P x n) – (G6P x n) --now divide by n

rG = G/n = F6P – G6P

Page 9: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

The Rxn Gibbs EnergyThe Rxn Gibbs Energy

rG = G/n = F6P – G6P

rG is the difference of the chemical potentials of the products and reactants at the composition of the rxn mixture

• We recognize that rG is the slope of the graph of the (changing) G vs composition of the system (Fig 7.1, p154)

rG = G/n = F6P – G6P

rG is the difference of the chemical potentials of the products and reactants at the composition of the rxn mixture

• We recognize that rG is the slope of the graph of the (changing) G vs composition of the system (Fig 7.1, p154)

Page 10: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

Effect of composition on rGEffect of composition on rG

• Fig 7.2 (154)• The relationship

of G to composition of the reactions

rG changes as n (the composition) changes

• Fig 7.2 (154)• The relationship

of G to composition of the reactions

rG changes as n (the composition) changes

Page 11: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

Reaction Gibbs energyReaction Gibbs energy

• Consider this reaction:aA + bB cC + dD

rG = (cC + dD) – (aA + bB)

μJtμJ+ RT ln aJ (derived in sec 6.6)

• Chemical potential (μ) changes as [J] changes

• The criterion for chemical equilibrium at constant T,P is: rG = 0 (7.2)

• Consider this reaction:aA + bB cC + dD

rG = (cC + dD) – (aA + bB)

μJtμJ+ RT ln aJ (derived in sec 6.6)

• Chemical potential (μ) changes as [J] changes

• The criterion for chemical equilibrium at constant T,P is: rG = 0 (7.2)

Page 12: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

Meaning of the value of rGMeaning of the value of rG

• Fig 7.3 (155)

• When is rG<0?

• When is rG=0?

• When is rG>0?

• What is the signifi-cance of each?

• Fig 7.3 (155)

• When is rG<0?

• When is rG=0?

• When is rG>0?

• What is the signifi-cance of each?

Page 13: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

Variation of rG with composition

Variation of rG with composition

For solutes in an ideal solution:

• aJ = [J]/c, the molar concentration of J relative to the standard value c = 1 mol/dm3

For perfect gases:

• aJ = pJ/p, the partial pressure of J relative to the standard pressure p = 1 bar

For pure solids and liquids, aJ = 1

For solutes in an ideal solution:

• aJ = [J]/c, the molar concentration of J relative to the standard value c = 1 mol/dm3

For perfect gases:

• aJ = pJ/p, the partial pressure of J relative to the standard pressure p = 1 bar

For pure solids and liquids, aJ = 1

p155f

Page 14: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

Variation of rG with composition

Variation of rG with composition

rG = (cC + dD) – (aA + bB) (7.1c)

rG = (cC + dD) – (aA + bB) (7.4a)

rG = {cGm(C)+dGm(D)} – {(aGm(A)+bGm(B)} (7.4b)

• 7.4a and 7.4b are the same

Is there an error in 7.1c in the textbook?

rG = (cC + dD) – (aA + bB) (7.1c)

rG = (cC + dD) – (aA + bB) (7.4a)

rG = {cGm(C)+dGm(D)} – {(aGm(A)+bGm(B)} (7.4b)

• 7.4a and 7.4b are the same

Is there an error in 7.1c in the textbook?

Page 15: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

Variation of rG with composition

Variation of rG with composition

rG = rG + RT ln rG = rG + RT ln aA aB

a b

aC aDc d

Q = aA aB

a b

aC aDc d

( )

rG = rG + RT ln Q

Since

Then

Page 16: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

Reactions at equilibriumReactions at equilibrium

• Again, consider this reaction:aA + bB cC + dD

• Q, arbitrary position; K, equilibrium• 0 = rG + RT ln K and rG = –RT ln K

• Again, consider this reaction:aA + bB cC + dD

• Q, arbitrary position; K, equilibrium• 0 = rG + RT ln K and rG = –RT ln K

Q = aA aB

a b

aC aDc d

K = aA aB

a b

aC aDc d

equilibrium( )

Page 17: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

Equilibrium constantEquilibrium constant

• With these equations….0 = rG + RT ln K

rG = –RT ln K (7.8)

• We can use values of rG from a data table to predict the equilibrium constant

• We can measure K of a reaction and calculate rG

• With these equations….0 = rG + RT ln K

rG = –RT ln K (7.8)

• We can use values of rG from a data table to predict the equilibrium constant

• We can measure K of a reaction and calculate rG

Page 18: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

Relationship between rG and KRelationship between rG and K

• Fig 7.4 (157)

• Remember, rG = –RT ln K

• So, ln K = –(rG/RT)

• If rG<0, then K>1; & products predominate at equilibrium

• And the rxn is thermo-dynamically feasible

• Fig 7.4 (157)

• Remember, rG = –RT ln K

• So, ln K = –(rG/RT)

• If rG<0, then K>1; & products predominate at equilibrium

• And the rxn is thermo-dynamically feasible At K > 1, rG < 0

At K = 1, rG = 0

At K < 1, rG > 0

Page 19: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

Relationship between rG and KRelationship between rG and K

• On the other hand…

• If rG>0, then K<1 and the reactants predominate at equilibrium…

• And the reaction is not thermo-dynamically feasible HOWEVER….

• Products will predominate over reactants significantly if K1 (>103)

• But even with a K<1 you may have products formed in some rxns

• On the other hand…

• If rG>0, then K<1 and the reactants predominate at equilibrium…

• And the reaction is not thermo-dynamically feasible HOWEVER….

• Products will predominate over reactants significantly if K1 (>103)

• But even with a K<1 you may have products formed in some rxns

Page 20: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

Relationship between rG and KRelationship between rG and K

• For an endothermic rxn to have rG<0, its rS>0; furthermore,

• Its temperature must be high enough for its TrS to be greater than rH

• The switch from rG>0 to rG<0 corresponds to the switch from K<1 to K>1

• This switch takes place at a temperature at which rH - TrS = 0, OR….

• For an endothermic rxn to have rG<0, its rS>0; furthermore,

• Its temperature must be high enough for its TrS to be greater than rH

• The switch from rG>0 to rG<0 corresponds to the switch from K<1 to K>1

• This switch takes place at a temperature at which rH - TrS = 0, OR….

T = rHrS

Page 21: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

Table 7.1 Thermodynamic criteria of spontaneity

Table 7.1 Thermodynamic criteria of spontaneity

G = H – TS

Page 22: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

Table 7.1 Thermodynamic criteria of spontaneity

Table 7.1 Thermodynamic criteria of spontaneity

G = H – TS

4. If H is positive and S is negative, G will always be positive—regardless of the temperature.

These two statements are an attempt to say the same thing.

Page 23: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

GG = = HH –– T TSS

1. If H is negative and S is positive, then G will always be negative regardless of temperature.

2. If H is negative and S is negative, then G will be negative only when TS is smaller in magnitude than H. This condition is met when T is small.

3. If both H and S are positive, then G will be negative only when the TS term is larger than H. This occurs only when T is large.

4. If H is positive and S is negative, G will always be positive—regardless of the temperature.

Page 24: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

GG = = HH –– TTSS

Factors Affecting the Sign of G

Page 25: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

Gibbs Free Energy (Gibbs Free Energy (GG))

For a constant-temperature process:

G = Hsys – TSsys

The change in Gibbs free energy (G)

18.4

If G is negative (G<0), there is a release of usable energy,

and the reaction is spontaneous!

If G is positive (G>0), the reaction is not spontaneous!

G = H – TS

All quantities in the above equation refer to the system

Page 26: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

For a constant-temperature process:

G = Hsys – TSsys

G < 0 The reaction is spontaneous in the forward direction.

G > 0 The reaction is nonspontaneous as written. The reaction is spontaneous in the reverse direction.

G = 0 The reaction is at equilibrium.

18.4

Gibbs Free Energy (Gibbs Free Energy (GG))

Page 27: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

aA + bB cC + dD

G0rxn dG0 (D)fcG0 (C)f= [ + ] – bG0 (B)faG0 (A)f[ + ]

G0rxn nG0 (products)f= mG0 (reactants)f–

The standard free-energy of reaction (G0 ) is the free-energy change for a reaction

when it occurs under standard-state conditions.

rxn

Gibbs Free Energy (Gibbs Free Energy (GG))

7.10

p158

Page 28: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

Who will explain this graph to the class?

Who will explain this graph to the class?

Page 29: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

Relationship between rG and KRelationship between rG and K

• For an endothermic rxn to have rG<0, its rS>0; furthermore,

• Its temperature must be high enough for its TrS to be greater than rH

• The switch from rG>0 to rG<0 corresponds to the switch from K<1 to K>1

• This switch takes place at a temperature at which rH - TrS = 0, OR….

• For an endothermic rxn to have rG<0, its rS>0; furthermore,

• Its temperature must be high enough for its TrS to be greater than rH

• The switch from rG>0 to rG<0 corresponds to the switch from K<1 to K>1

• This switch takes place at a temperature at which rH - TrS = 0, OR….

T = rHrS

Page 30: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

Reactions at equilibriumReactions at equilibrium

• Fig 7.5 (162)• An endothermic

rxn with K>1 must have T high enough so that the result of subtract-ing TrS from rH is negative

• Or rH–TrS < 0

• Set rH–TrS=0 and solve for T

• Fig 7.5 (162)• An endothermic

rxn with K>1 must have T high enough so that the result of subtract-ing TrS from rH is negative

• Or rH–TrS < 0

• Set rH–TrS=0 and solve for T

T = rHrS

equilibrium

rG = rH – TrS

Page 31: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

Reactions at equilibriumReactions at equilibrium

equilibrium

rG = rH – TrS

Page 32: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

Table 7.2 Table 7.2 Standard Gibbs energies of Standard Gibbs energies of formation at 298.15 K* (gases)formation at 298.15 K* (gases)

Table 7.2 Table 7.2 Standard Gibbs energies of Standard Gibbs energies of formation at 298.15 K* (gases)formation at 298.15 K* (gases)

Page 33: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

Table 7.2 Standard Gibbs energies of formation at 298.15 K* (liquids & solids)

Table 7.2 Standard Gibbs energies of formation at 298.15 K* (liquids & solids)

Page 34: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

Standard Gibbs Energy of Formation

Standard Gibbs Energy of Formation

• Fig 7.6 (159)• Analogous to

altitude above or below sea level

• Units of kJ/mol

• Fig 7.6 (159)• Analogous to

altitude above or below sea level

• Units of kJ/mol

Page 35: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

The equilibrium compositionThe equilibrium composition

• The magnitude of K is a qualitative indicator

• If K 1 (>103) then rG < –17 kJ/mol @ 25ºC, the rxn has a strong tendency to form products

• If K 1 (<10–3) then rG > +17 kJ/mol @ 25ºC, the rxn will remain mostly unchanged reactants

• If K 1 (10–3-103), then rG is between –17 to +17 kJ/mol @ 25ºC, and the rxn will have significant concentrations of both reactants and products

• The magnitude of K is a qualitative indicator

• If K 1 (>103) then rG < –17 kJ/mol @ 25ºC, the rxn has a strong tendency to form products

• If K 1 (<10–3) then rG > +17 kJ/mol @ 25ºC, the rxn will remain mostly unchanged reactants

• If K 1 (10–3-103), then rG is between –17 to +17 kJ/mol @ 25ºC, and the rxn will have significant concentrations of both reactants and products p.160

Page 36: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

Calculating an equilibrium concentration

Calculating an equilibrium concentration

•Example 7.1 (p165)

•Example 7.2 (p166)

•Example 7.1 (p165)

•Example 7.2 (p166)

Page 37: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

Standard reaction Gibbs energyStandard reaction Gibbs energy

rG = Gm(products) – Gm(reactants)

rG = rH – TrS

rG = Gm(products) – Gm(reactants)

rG = rH – TrS

Page 38: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

7.6 Kc and Kp 7.6 Kc and Kp

aA + bB cC + dD

Kc = [C]c[D]d

[A]a[B]b

In most cases

Kc Kp

aA (g) + bB (g) cC (g) + dD (g)

Kp = Kc(RT)n

Kp = pC

dpD

pA pBa b

c

Kp = Kc(RT)n

When does Kp = Kc ?

Page 39: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

Derivation 7.1: Kc and Kp Derivation 7.1: Kc and Kp

Atkins uses

Work through Derivation 7.1, p.162

K = Kc cRT

p ][vgas

K = Kc T

12.07K ][vgas

Substituting values for c, p, and R, we get

What is this K?

What is vgas?

Page 40: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

Coupled reactionsCoupled reactions

• Box 7.1 (164)• Weights as analogy

to rxns• A rxn with a large

rG can force another rxn with a smaller rG to run in its nonspontan-eous direction

• Enzymes couple biochemical rxns

• Box 7.1 (164)• Weights as analogy

to rxns• A rxn with a large

rG can force another rxn with a smaller rG to run in its nonspontan-eous direction

• Enzymes couple biochemical rxns

Page 41: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

Coupled reactionsCoupled reactions

• Biological standard state (pH = 7)• Typical symbols for standard state:

¤ ´ °

Read the last paragraph in Box 7.1 on p164 regarding ATP and the “high energy” bond

• Biological standard state (pH = 7)• Typical symbols for standard state:

¤ ´ °

Read the last paragraph in Box 7.1 on p164 regarding ATP and the “high energy” bond

Page 42: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

Equilibrium response to conditions

Equilibrium response to conditions

• What effect will a change in temperature, in pressure, or the presence of a catalyst have on the equilibrium position?

• Presence of a catalyst? None. Why?

rG is unchanged, so K is not changed

• How about a change in temperature? • Or a change in pressure? Let’s see…

• What effect will a change in temperature, in pressure, or the presence of a catalyst have on the equilibrium position?

• Presence of a catalyst? None. Why?

rG is unchanged, so K is not changed

• How about a change in temperature? • Or a change in pressure? Let’s see…

Page 43: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

The effect of temperatureThe effect of temperature

• Fig 7.7 (163) rG of a rxn that

results in fewer moles of gas increases with increasing T

rG of a rxn with no net change…

rG of a rxn that produces more moles of gas decreases with increasing T

• Fig 7.7 (163) rG of a rxn that

results in fewer moles of gas increases with increasing T

rG of a rxn with no net change…

rG of a rxn that produces more moles of gas decreases with increasing T

Page 44: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

Equilibrium response to conditions

Equilibrium response to conditions

• Le Chatelier’s principle suggests

When a system at equilibrium is compressed, the composition of a gas-phase equilibrium adjusts so as to reduce the number of molecules in the gas phase

• Le Chatelier’s principle suggests

When a system at equilibrium is compressed, the composition of a gas-phase equilibrium adjusts so as to reduce the number of molecules in the gas phase

p.172

Page 45: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

The effect of pressureThe effect of pressure

• Fig 7.9 (174)• A change in

pressure does not change the value of K, but it does have other consequences (composition)

• As p0, xHI1

• What is [I2]?

• Fig 7.9 (174)• A change in

pressure does not change the value of K, but it does have other consequences (composition)

• As p0, xHI1

• What is [I2]?

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

Page 46: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

Key Key IdeasIdeas

Page 47: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

Key Key IdeasIdeas

Page 48: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

The EndThe End…of this chapter…”…of this chapter…”

Page 49: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

Spare parts to copy and pasteSpare parts to copy and paste

• μJtμJ+RT ln aJ

• Chemical potential (μ) changes as [J] changes

• μJtμJ+RT ln aJ

• Chemical potential (μ) changes as [J] changes

Page 50: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

Box 7.1 pp.172fBox 7.1 pp.172f

• O2 binding in hemoglobin and myoglobin…

• …In resting tissue and in lung tissue

• O2 binding in hemoglobin and myoglobin…

• …In resting tissue and in lung tissue

Page 51: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

Chemical PotentialChemical Potential

• Review pp.128-130, Partial molar properties (e.g. partial molar volume)

• Read p.129, last two paragraphs• Read handout, “Chemical Potential” by

Philip A. Candela• Chemical potential ( ) is usually

described as the “partial molar Gibbs function” or “partial molar Gibbs energy”

• Review pp.128-130, Partial molar properties (e.g. partial molar volume)

• Read p.129, last two paragraphs• Read handout, “Chemical Potential” by

Philip A. Candela• Chemical potential ( ) is usually

described as the “partial molar Gibbs function” or “partial molar Gibbs energy”

Page 52: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

Chemical PotentialChemical Potential

• The quantity G/n is so important that it is given a special symbol () and its own name (chemical potential)

• As the symbols G/n above indicate, chemical potential is the Gibbs free energy per mole of substance

• The chemical potential is an indication of the potential of a substance to be chemically active (p.130)

• The quantity G/n is so important that it is given a special symbol () and its own name (chemical potential)

• As the symbols G/n above indicate, chemical potential is the Gibbs free energy per mole of substance

• The chemical potential is an indication of the potential of a substance to be chemically active (p.130)

Page 53: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

Excursus: Chemical PotentialExcursus: Chemical Potential

• The standard chemical potential of a gas (μJ), is identical to its standard molar Gibbs energy (Gm) at 1 bar

• The greater the partial pressure of a gas, the greater its chemical potential

• The standard chemical potential of a gas (μJ), is identical to its standard molar Gibbs energy (Gm) at 1 bar

• The greater the partial pressure of a gas, the greater its chemical potential

Page 54: Atkins & de Paula: Elements of Physical Chemistry: 5e Chapter 7: Chemical Equilibrium: The Principles Chapter 7: Chemical Equilibrium: The Principles

Excursus: Chemical PotentialExcursus: Chemical Potential

• Common expressions of chemical potential:

μJtμJ+ RT ln aJ

μJtμJ+ RT ln

μJtμJ+ RT ln p

• Common expressions of chemical potential:

μJtμJ+ RT ln aJ

μJtμJ+ RT ln

μJtμJ+ RT ln p

p

p

p = 1 bar