Dynamic Equilibrium

Reversible (closed system)

Forward Rate, K1 Reverse Rate, K-1

Conc of product and reactant at equilibrium

At Equilibrium

Forward rate = Backward rate Conc reactants and products remain CONSTANT/UNCHANGE

Equilibrium Constant Kc

aA(aq) + bB(aq) cC(aq) + dD(aq)

coefficient

Solid/liq not included in Kc Conc represented by [ ]

K1

K-1

ba

dc

cBA

DCK

1

1

K

KKc

Equilibrium Constant Kc

express in

Conc vs time Rate vs time

A + B

C + D

Conc

Time

reversetconsrate

forwardtconsrate

K

K

..tan..

..tan..

1

1

Catalyst

Factors affecting equilibrium (closed system)

Temperature Pressure Concentration

Equilibrium constant Kc ≠ Position equilibrium

Factors affecting the position of Equilibrium

Effect of Concentration on the position of equilibrium

Increase Conc SCN- or Fe3+ •Equilibrium shift to right → •Formation of complex ion Fe(SCN)2+ (red blood)

Fe3+ + SCN- ↔ Fe(SCN)+2

(yellow) (red Blood)

Increase Concentration • Rate of rxn increase ↑ • Position of equilibrium shift to a side to decrease conc again ↓

• Kc, equilibrium constant - no change • Rate constant, forward/backward - no change

Decrease Conc Fe3+ • By adding OH- will shift equilibrium to left ←

•Fe(SCN)2+ breakdown to form more Fe3+ (yellow)

Decrease Conc SCN- • By adding Ag+ will shift equilibrium to left • Fe(SCN)2+ breakdown to form more SCN- (yellow)

• Increase Conc ↑ - position of equilibrium shift to right/left - Conc is Reduced ↓ • Decrease Conc ↓ – position of equilibrium shift to right/left - Conc is Increased ↑

Click to view video

Le Chatelier’s Principle • System in dynamic equilibrium is disturbed, the position of equilibrium will shift so as to cancel out the effect of change and a new equilibrium can be established again

Effect of Concentration on the position of equilibrium

Decrease Conc H+ • By adding OH- •Equilibrium shift to left ← •Formation of CrO4

2- (yellow)

Increase Conc H+ • By adding H+ • Shift equilibrium to right → • Formation of Cr2O7

2- (orange)

2CrO42- + 2H+ ↔ Cr2O7

2- + H2O (yellow) (orange)

Click to view video

Factors affecting the position of Equilibrium

• Increase Conc ↑ - position of equilibrium shift to right/left - Conc is Reduced ↓ • Decrease Conc ↓ – position of equilibrium shift to right/left - Conc is Increased ↑

Increase Concentration • Rate of rxn increase ↑ • Position of equilibrium shift to a side to decrease conc again ↓

• Kc, equilibrium constant - no change • Rate constant, forward/backward - no change

Le Chatelier’s Principle • System in dynamic equilibrium is disturbed, the position of equilibrium will shift so as to cancel out the effect of change and a new equilibrium can be established again

Effect of Concentration on the position of equilibrium

Decrease Conc CI- •Adding Ag+ to form AgCI •Equilibrium shift to right → •Formation of Co(H2O)6

2+ (pink)

Increase Conc CI- • Adding HCI • Shift equilibrium to left ← • Formation of CoCl4

2- (blue)

CoCl42- + 6H2O ↔ Co(H2O)6

2+ + 4CI –

(blue) (pink)

Increase Conc H2O • Adding H2O • Shift equilibrium to right → • Formation of Co(H2O)6

2+ (pink)

Click to view video

Factors affecting the position of Equilibrium

• Increase Conc ↑ - position of equilibrium shift to right/left - Conc is Reduced ↓ • Decrease Conc ↓ – position of equilibrium shift to right/left - Conc is Increased ↑

Increase Concentration • Rate of rxn increase ↑ • Position of equilibrium shift to a side to decrease conc again ↓

• Kc, equilibrium constant - no change • Rate constant, forward/backward - no change

Le Chatelier’s Principle • System in dynamic equilibrium is disturbed, the position of equilibrium will shift so as to cancel out the effect of change and a new equilibrium can be established again

Effect of Pressure on the position of equilibrium

Increasing Pressure ↑ • By reducing Vol • Equilibrium shift to left ← • Less molecule on left side •Pressure drop ↓ • Formation N2O4(colourless)

Increase pressure ↑ - favour rxn with a decrease ↓in pressure/number of molecule Decrease pressure ↓ - favour rxn with a increase ↑ in pressure/number of molecule

Decreasing Pressure ↓ • By Increasing Vol • Equilibrium shift to right → • More molecule on right side •Pressure increase ↑ • Formation NO2 (brown)

Increase pressure ↑ – collision more frequent - shift equilibrium to left - reduce number of molecule - pressure decrease again ↓ Decrease pressure ↓ – collision less frequent – shift equilibrium to right – increase number of molecule – pressure increase again ↑

Click to view video

Factors affecting the position of Equilibrium

Le Chatelier’s Principle • System in dynamic equilibrium is disturbed, the position of equilibrium will shift so as to cancel out the effect of change and a new equilibrium can be established again

N2O4(g) ↔ 2NO2(g) (colourless) (brown)

Increase Pressure • Rate of rxn increase ↑ • Position of equilibrium shift to a side to decrease pressure again ↓

• Kc, equilibrium constant - no change • Rate constant, forward/backward - no change

Reduce Vol Increase Vol

Mole ratio 1(left) ↔ 2(right)

Effect of Pressure on the position of equilibrium

N2(g) + 3H2(g) ↔ 2NH3(g)

( 4 vol/mole ) (2 vol/mole)

Increasing Pressure ↑ • Equilibrium shift to right → • Less molecule on left side •Pressure drops ↓ • Formation of NH3 (product)

Decreasing Pressure ↓ • Equilibrium shift to left ← • More molecule on right side •Pressure increase ↑ • Formation H2 and N2 (reactant)

Click to view video

Factors affecting the position of Equilibrium

Increase pressure ↑ - favour rxn with a decrease ↓in pressure/number of molecule Decrease pressure ↓ - favour rxn with a increase ↑ in pressure/number of molecule

N2O4(g) ↔ 2NO2(g) (colourless) (brown)

Increasing Pressure ↑ • By reducing Vol • Equilibrium shift to left ← • Less molecule on left side •Pressure drop ↓ • Formation N2O4(colourless)

Decreasing Pressure ↓ • By Increasing Vol • Equilibrium shift to right → • More molecule on right side •Pressure increase ↑ • Formation NO2 (brown)

Mole ratio 1(left) ↔ 2(right)

Mole ratio 4(left) ↔ 2(right)

Reduce Vol Increase Vol

Effect of Temperature on position of equilibrium

Decrease Temp ↓ • Cooling it down • Favour exothermic rxn • Equilibrium shift to right → • Increase Temp ↑ again • Formation Co(H2O)6

2+ (pink)

Increase Temp ↑ • Heating it up • Favour endothermic rxn • Equilibrium shift to left ← • Reduce Temp ↓ again • Formation of CoCl4

2- (blue)

CoCl42- + 6H2O ↔ Co(H2O)6

2+ + 4CI – ΔH = -ve (exothermic)

(blue) (pink)

Increase Temp ↑ – Favour endothermic rxn – Absorb heat to reduce Temp again ↓ Decrease Temp ↓ – Favour exothermic rxn – Release heat to increase Temp again ↑

Increase Temperature • Rate of rxn increase • Rate constant also change • Rate of forward/reverse increase but to diff extend • Position equilibrium shift to endo to decrease Temp • Kc, equilibrium constant change

Click to view video

Factors affecting the position of Equilibrium

Le Chatelier’s Principle • System in dynamic equilibrium is disturbed, the position of equilibrium will shift so as to cancel out the effect of change and a new equilibrium can be established again

Decrease Temp ↓ • Cooling it down ↓ • Favour exothermic rxn • Equilibrium shift to left ← • Increase Temp ↑ • Formation N2O4 (colourless)

Increase Temp ↑ • Heating it up ↑ • Favour endothermic rxn • Equilibrium shift to right → • Reduce Temp ↓ • Formation NO2

(brown)

N2O4 (g) ↔ 2NO2(g) ΔH = + 54kJmol-1

(colourless) (brown)

Click to view video

Factors affecting the position of Equilibrium

Le Chatelier’s Principle • System in dynamic equilibrium is disturbed, the position of equilibrium will shift so as to cancel out the effect of change and a new equilibrium can be established again

Effect of Temperature on position of equilibrium

Increase Temp ↑ – Favour endothermic rxn – Absorb heat to reduce Temp again ↓ Decrease Temp ↓ – Favour exothermic rxn – Release heat to increase Temp again ↑

Increase Temperature • Rate of rxn increase • Rate constant also change • Rate of forward/reverse increase but to diff extend • Position equilibrium shift to endo to decrease Temp • Kc, equilibrium constant change

Catalyst • Provide an alternative pathway with lower activation energy • Increase forward and reverse rate to the same extent/factor • Position of equilibrium and Kc UNCHANGED • Catalyst shorten time to reach equilibrium

Effect of Catalyst on equilibrium constant, Kc

Without catalyst Reach equilibrium slow

With catalyst Reach equilibrium fast

Effect catalyst on Rate, Rate constant and Kc – NH3 production

N2(g) + 3H2(g) ↔ 2NH3(g) ΔH = - 92kJmol-1

Factors affecting the position of Equilibrium

Forward rate

Reverse rate

Catalyst • Rate of rxn increase •Forward/reverse rate increase to SAME extend • Kc equilibrium constant NO change •Position equilibrium NO change •Product/reactant yield NO change

Catalyst

Effect of catalyst on Rate of Reaction

Catalyst • Provide alternative pathway with lower activation energy • Greater proportion of colliding molecule with energy greater than > Ea • Rate increase

Source : http://njms2.umdnj.edu/biochweb/education/bioweb/PreK2010/EnzymeProperties.html

Catalyst • Provide alternative pathway with lower activation energy • Fraction of molecule with energy greater than > Ea increase • Rate increase

Maxwell Boltzmann Energy distribution curve Without catalyst With catalyst

Without catalyst

Maxwell Boltzmann Energy distribution curve

Fraction molecules energy > Ea

Fraction – lead to product formation

How position equilibrium shift when H2 is added ?

N2(g) + 3H2(g) ↔ 2NH3(g)

07.4cK

Qualitatively (prediction) Quatitatively

Le Chatelier’s Principle

At equilibrium Conc reactant/product no change

Equilibrium disturbed H2 added. More reactant

N2(g) + 3H2(g) ↔ 2NH3(g)

Position equilibrium shift to right - Reduce conc H2

- More product form

Shift to right

Qc and Kc

At equilibrium Conc reactant/product no change

Equilibrium disturb H2 added.

New equilibrium Conc reactant/product no change

Eq Conc H2 = 0.82 Eq Conc N2 = 0.20 Eq Conc NH3= 0.67

New Conc H2 = 1.00 Conc N2 = 0.20 Conc NH3 = 0.67

New Eq Conc H2 = 0.90 New Eq Conc N2 = 0.19 New Eq Conc NH3 = 0.75

32

1

2

2

3

HN

NHKc

31

2

82.020.0

67.0cK

07.4cK

32

1

2

2

3

HN

NHQc

31

2

00.120.0

67.0cQ

24.2cQ

32

1

2

2

3

HN

NHKc

31

2

90.019.0

75.0cK

07.4cK

Shift to the right

- Increase product

- Qc = Kc again

Factors affecting the position of Equilibrium

Effect of Temperature on equilibrium constant, Kc

N2O4 (g) ↔ 2NO2(g) ΔH = + 54kJmol-1

Temp increase ↑ – Kc increase ↑

A B ΔH = +ve Rate reverse = k r

Rate forward = kf

Kc

A

BK c

r

f

cK

KK

reversetconsrate

forwardtconsrate

K

K

r

f

..tan..

..tan..

Temp affect rate constant

Temp changes

cK

Increase Temp ↑

Position equilibrium shift to right Endo side – Absorb heat Temp decrease ↓

More product , less reactant treac

productK c

tan

cKForward rate constant, kf > reverse rate, kr

r

f

cK

KK

Decrease Temp ↓

Position equilibrium shift to left Exo side – Release heat Temp increase ↑

More reactant , less product treac

productKc

tan

Forward rate constant, kf < reverse rate, kr

r

f

cK

KK

cK

Conclusion : Endo rxn – Temp ↑ – Kc ↑ – Product ↑

A B ΔH = -ve

Factors affecting the position of Equilibrium

Effect of Temperature on equilibrium constant, Kc

Temp increase ↑ – Kc decrease ↓

Rate reverse = k r

Rate forward = kf

Kc

A

BK c

r

f

cK

KK

reversetconsrate

forwardtconsrate

K

K

r

f

..tan..

..tan..

Temp affect rate constant

Temp changes

cK

Increase Temp ↑

Position equilibrium shift to left Endo side – Absorb heat Temp decrease ↓

More Reactant, less product treac

productK c

tan

cKForward rate constant, kf < Reverse rate, kr

r

f

cK

KK

Decrease Temp ↓

Position equilibrium shift to right Exo side – Release heat Temp increase ↑

More Product , less reactant treac

productKc

tan

Forward rate constant, kf > Reverse rate, kr

r

f

cK

KK

cK

Conclusion : Exo rxn – Temp ↑ – Kc ↓ – Product ↓

H2(g) + I2(g) ↔ 2HI(g) ΔH = -9.6kJmol-1

N2(g) + 3H2(g) ↔ 2NH3(g) ΔH = - 92kJmol-1

Haber process • Production ammonia making fertiliser • Reversible process N2(g) + 3H2(g) ↔ 2NH3(g) • Optimum yield conditions are : Pressure – 400 atm, Temp – 400C, Catalyst - Iron

Application Equilibrium constant Kc and Kinetic in Industry (NH3 Production)

Highest yield, HIGH Kc, HIGH Rate, Low cost

Increase yield (NH3) – Position equilibrium shift to right →

Low Temp ↓ •Position shift right (exo) - Release heat – Temp ↑ •Low ↓ Temp – Yield NH3 high ↑ BUT Rate slow

High Pressure ↑ - Position shift right - less mole of gas – Pressure ↓ - High ↑ Pressure – Yield NH3 high – BUT cost high (Not economical)

High Yield Conditions • Low temperature ↓ but rate slow

• High Pressure ↑ but too expensive

• Not economical

Industry Conditions • Compromise Temp -400C

• Pressure - 400atm

• Catalyst iron – Increase Rate • Remove NH3 produced, equilibrium

shift to right →

Effect of Temperature, Catalyst and Pressure on Haber Process

Temperature Pressure

cK

Rate

Cost

Ideal conditions Practical/Industry conditions

Highest yield, HIGH Kc, HIGH Rate, Low cost

Increase yield (H2SO4) – Position equilibrium shift to right →

High Yield Conditions • Low temperature ↓ but rate slow

• High Pressure ↑ but too expensive

• Not economical

Temperature Pressure

Contact process • Production sulphuric acid • Process involve 3 stages Stage 1 – S + O2 (g) → SO2(g) Stage 2 - 2SO2(g) + O2(g) ↔ 2SO3(g) Stage 3 – SO3(g) + H2O → H2SO4

2SO2(g) + O2(g) ↔ 2SO3(g) ΔH = - 197kJmol-1

Industry Conditions • Compromise Temp - 450C

• Pressure of 2atm

• Catalyst vanadium(V) oxide V2O5

• Remove SO3 produced, equilibrium

shift to right →

Effect of Temperature, Catalyst and Pressure on Contact Process

Application Equilibrium constant Kc and Kinetic in Industry (H2SO4 Production)

cK

Rate

Cost

Low Temp ↓ •Position shift right (exo) - Release heat – Temp ↑ •Low ↓ Temp – Yield NH3 high BUT Rate slow

High Pressure ↑ - Position shift right - less mole of gas – Pressure ↓ - High ↑ Pressure – Yield NH3 high – BUT cost high (Not economical)

Ideal conditions Practical/Industry conditions

Low temp

IB Questions

Which of rxn not affected by change in pressure?

4NH3(g) + 5O2(g) ↔ 4NO(g) + 6H2O(g)

N2(g) + 3H2(g) ↔ 2NH3(g) H2(g) + I2(g) ↔ 2HI(g)

2SO2(g) + O2(g) ↔ 2SO3(g)

CO is toxic. Rxn take place in catalytic converter. At equilibrium, will CO increase, decrease or unchanged a) Pressure increase/by decreasing vol b) Pressure increase by adding O2

c) Temp increase d) Platinum catalyst added

CaCO3(s) ↔ CaO(g) + CO2(g)

CH3COOH(l) + C2H5OH(l) ↔ CH3COOC2H5(l) + H2O(l)

CuO(s) + H2(g) ↔ Cu(s) + H2O(g) 2CO(g) + O2(g) ↔ 2CO2(g)

a) Shift to right – decrease number molecule ↓ -CO decrease ↓ b) Shift to right – decrease conc O2 ↓ - CO decrease ↓ c) Shift to left –endo rxn – decrease ↓ temp again -CO increase ↓ d) NO change

Ex 1 Ex 2 Ex 3

Mole ratio 4(left) ↔ 2(right) Mole ratio 2(left) ↔ 2(right) Mole ratio 2(left) ↔ 2(right)

Ex 4 Ex 5 Ex 6

Mole ratio 0(left) ↔ 2(right) Mole ratio 3(left) ↔ 2(right) Mole ratio 9(left) ↔ 10(right)

Ex 7 Ex 8

Mole ratio 3(left) ↔ 2(right) Mole ratio 1(left) ↔ 1(right)

Solid not included

Solid not included

Ex 9 2CO(g) + O2(g) ↔ 2CO2(g) ΔH = -566kJmol-1 Reversible rxn bet hydrogen and iodine shown below Ex 10

H2 + I2 ↔ 2HI

a) Outline characteristic of homogenous sys in equilibrium b) Predict the position eq when pressure increase from 1 to 2 atm c) Kc at 500k - 160. Kc at 700K - 54. Deduce the enthalpy of forward rxn. d) 1.60 mol H2 and 1 mol I2 allowed to reach equilibrium in 4 dm3

vessel. Amt HI formed at eq is 1.8 mol. Find Kc

a) Reactant/product on same phase, Rate forward = Rate reverse Conc reactant/product unchanged. Macroscopic property (same) b) No change in position equilibrium (molecules both sides same) c) Rxn exo/heat given out. H = -ve d) Moles- H2 = 1.6 – 0.9 = 0.7, I2 = 1 – 0.9 = 0.1, HI = 1.8

12

1

2

2

IH

HIKc

11

2

1.07.0

8.1cK

Eq amt used instead eq conc

3.46cK