IB Chemistry on Dynamic Equilibrium and Equilibrium Constant

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Dynamic Equilibrium Chemical Reaction Reversible Irreversible A C Open system Limiting reactants used up. Reaction stop E a low, energetic/kinetic favourable -ΔH C A C Closed system (No matter escapes) Forward rxn – products Reverse rxn - reactants Product dissociate form reactant C Reaction going on Reaction stop Open system Unidirection A C Closed system - No matter escape Both direction - equilibrium A C Both forward and reverse rxn continue at equilibrium Movement of particles bet both sides goes on Conc of reactants and products remain constant Rate of forward = Rate of reverse Formation and decomposition continues Two/more opposing rxn take place same time, same rate At dynamic equilibrium Conc remain constant Vs A A Photo: http://declanfleming.com/man-vs-escalator-equilibrium-model/ http://chemistry.tutorvista.com/physical-chemistry/reversible-reaction-and-irreversibility.html

Transcript of IB Chemistry on Dynamic Equilibrium and Equilibrium Constant

Page 1: IB Chemistry on Dynamic Equilibrium and Equilibrium Constant

Dynamic Equilibrium

Chemical Reaction

Reversible Irreversible

A C

• Open system • Limiting reactants used up. • Reaction stop • Ea low, energetic/kinetic favourable -ΔH

C

A C

• Closed system (No matter escapes) • Forward rxn – products • Reverse rxn - reactants • Product dissociate form reactant

C

Reaction going on Reaction stop

Open system Unidirection

A

C

Closed system - No matter escape Both direction - equilibrium

A

C

• Both forward and reverse rxn continue at equilibrium • Movement of particles bet both sides goes on • Conc of reactants and products remain constant Rate of forward = Rate of reverse • Formation and decomposition continues • Two/more opposing rxn take place same time, same rate

At dynamic equilibrium

Conc remain constant Vs

A A

Photo: http://declanfleming.com/man-vs-escalator-equilibrium-model/

http://chemistry.tutorvista.com/physical-chemistry/reversible-reaction-and-irreversibility.html

Page 2: IB Chemistry on Dynamic Equilibrium and Equilibrium Constant

Dynamic Equilibrium

Closed system

Reversible

Forward Rate, Kf

Reverse Rate, Kr

Liquid -Vapour equilibrium Br2(l) ↔ Br2(g)

initial equilibrium

• Liq and gas Br2 in dynamic equilibrium • Add more liq Br2 will increase its liq mass but not conc • Dynamic equilibrium, Kc bet liq and gas Br2 remain the same • Macroscopic level – colour/intensity liq/gas Br2 remain constant • Microscopic level – liq/gas Br2 equilibrium, forward/ reverse rxn going on (Rate of Vapourization = Rate of Condensation)

NO change in conc liquid/vapour

Rate of evaporation = Rate of condensation

Rate of evaporation > Rate of condensation

More vapour form

Rate condensation increase

Initially

Br2 (l) Br2(g)

time

Rate

Rate of

condensation

Rate of

evaporation

Why add more liq Br2 will not change intensity

vapour?

Remove Br2 gas - Conc Br2 gas change - affect Kc (Rate of Vapourization > Rate of Condensation)

Density = Mass Vol

Conc = Mass

Vol More mass - more vol Density/conc still same

Rate of vapourization/condensation depend on change in conc Br2

(Rate of Vapourization = Rate of Condensation) No change in conc/intensity vapour Br2

Add more Br2

Page 3: IB Chemistry on Dynamic Equilibrium and Equilibrium Constant

Dynamic Equilibrium

Closed system

Reversible

Forward Rate, Kf

Reverse Rate, Kr

initial equilibrium

NO change in conc sugar sol

Rate of dissolving = Rate of crystallization

Rate of dissolving > Rate of crystallization

More sugar dissolve - saturated sol form

Rate crystallization increase

Initially

time

Rate

Rate of

crystallization

Rate of

dissolving

Why add more sugar will not change

sweetness/conc?

Solute-solution equilibrium Sugar(s) ↔ Sugar (aq)

• Sugar crystals/solution in dynamic equilibrium • Add sugar will not increase sugar conc/sweetness (saturated sol) • Dynamic equilibrium, Kc bet sugar solid and sol remain same • Macroscopic level – conc/sweetness remain constant • Microscopic level – crystal/sol in equilibrium, forward/reverse rxn going on (Rate of Dissolving = Rate of Crystallization)

Adding more water – affect Kc – Conc sugar changes ( Rate of Dissolving > Rate of Crystallization )

Sugar (s) Sugar (aq)

Add more sugar

More mass - more vol Density/conc still same

Conc = Mass

Vol

Density = Mass Vol

Rate of dissolving/crystallization depend on change in sugar conc

(Rate of Dissolving = Rate of Crystallization) No change in sugar conc (solution)

Page 4: IB Chemistry on Dynamic Equilibrium and Equilibrium Constant

Dynamic Equilibrium

Closed system

Reversible

Forward Rate, Kf

Reverse Rate, Kr

initial equilibrium

NO change in conc vapour

Rate of vapourization = Rate of crystallization

Rate of vapourization > Rate of crystallization

More iodine sublime

Rate crystallization increase

Initially

time

Rate

Rate of

crystallization

Rate of

vapourization

Why add more I2 will not change vapour

pressure/intensity?

Solid-vapour equilibrium Iodine(s) ↔ Vapour(g)

• I2 solid/vapour in dynamic equilibrium • Add more I2 will not increase vapour pressure I2 • Equilibrium, Kc bet solid/vapour remain the same (Temp dependent) • Macroscopic level – Vapour pressure/intensity remain constant • Microscopic level – solid/vapour in equilibrium, forward/reverse rxn going on (Rate of Vapourization = Rate of Crystallization)

Using a bigger container. Will vapour pressure change?

Iodine (s) Iodine (g)

Add more I2

More mass - more vol Density/conc still same

Conc = Mass

Vol

Density = Mass Vol

Rate of vapourization/crystallization depend on change in conc I2 (Temp dependent)

(Rate of Vapourization = Rate of Crystallization)

Vapour pressure same

Page 5: IB Chemistry on Dynamic Equilibrium and Equilibrium Constant

Dynamic Equilibrium

Closed system

Reversible

Forward Rate, Kf

Reverse Rate, Kr

Liquid -Vapour equilibrium Br2(l) ↔ Br2(g)

initial equilibrium

NO change in conc liquid/intensity vapour/vapour pressure

Rate of evaporation = Rate of condensation

Liquid Br2 evaporate

Macroscopic – no changes

2NO2(g) N2O4(g)

Physical system Chemical system

Vapour Br2 condense Forward rate rxn Rate Combining

Backward rate rxn Rate decomposition

Reversible rxn happening, same time with same rate

Rate of forward = Rate of backward

Conc of reactants and products remain UNCHANGED not EQUAL

combining decomposition

brown colourless

Page 6: IB Chemistry on Dynamic Equilibrium and Equilibrium Constant

Dynamic Equilibrium

Closed system

Reversible

Forward Rate, Kf

Reverse Rate, Kr

2NO2(g) N2O4(g)

Chemical system

Forward rate rxn Rate Combining

Backward rate rxn Rate dissociation

Reversible rxn happening, same time with same rate

Rate of forward = Rate of backward

Conc of reactant and product remain UNCHANGED/CONSTANT not EQUAL

combining dissociation

Conc vs time Rate vs time

Conc

Time

Conc NO2

Conc N2O4

With time • Conc NO2 decrease ↓ - Forward rate decrease ↓

• Conc N2O4 increase ↑ - Backward rate increase ↑

2NO2(g) N2O4(g)

Forward rate

Backward rate

Forward Rate = Backward Rate

Conc NO2 and N2O4 remain UNCHANGED/CONSTANT

brown colourless

Page 7: IB Chemistry on Dynamic Equilibrium and Equilibrium Constant

How dynamic equilibrium is achieved in closed system?

Conc of NO2 decrease ↓over time

Forward rate, Kf decrease ↓ over time

Forward Rate = Reverse Rate

NO2

2NO2(g) N2O4(g)

Conc of N2O4 increase ↑ over time

N2O4

Reverse rate, Kr increase ↑ over time

NO2

N2O4

1

2

Conc of reactant/product remain constant

Rate

3

Time

Conc

NO2

N2O4

At dynamic equilibrium

As reaction proceeds concentration

As reaction proceeds rate

Time

Page 8: IB Chemistry on Dynamic Equilibrium and Equilibrium Constant

Dynamic Equilibrium

Reversible (closed system)

Forward Rate, K1 Reverse Rate, K-1

Kc = ratio of molar conc of product (raised to power of their respective stoichiometry coefficient) to molar conc of reactant (raised to power of their respective stoichiometry coefficient)

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

Click here notes on dynamic equilibrium

Excellent Notes

K1 = forward rate constant

K-1 = reverse rate constant

Page 9: IB Chemistry on Dynamic Equilibrium and Equilibrium Constant

Large Kc

• Position equilibrium shift to right • More product > reactant

Magnitude of Kc

ba

dc

cBA

DCK

Extend of reaction

How far rxn shift to right or left?

Not how fast

ba

dc

cBA

DCK

Small Kc

• Position equilibrium shift to left • More reactant > product

cKcK

Position of equilibrium

2CO2(g) ↔ 2CO(g) + O2(g)

92103 cK

2H2(g) + O2(g) ↔ 2H2O(g)

81103cK

H2(g) + I2(g) ↔ 2HI(g)

2107.8 cK1

Moderate Kc

• Position equilibrium lies slightly right • Reactant and product equal amount

Reaction completion

Product favoured Reactant favoured Reactant/Product equal

cK

Temp dependent

Extend of rxn

Not how fast

Page 10: IB Chemistry on Dynamic Equilibrium and Equilibrium Constant

Equilibrium Constant Kc

ba

dc

cBA

DCK

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

Conc of product and reactant at equilibrium

Equilibrium expression HOMOGENEOUS gaseous rxn

4NH3(g) + 5O2(g) ↔ 4NO(g) + 6H2O(g) N2(g) + 3H2(g) ↔ 2NH3(g)

NH4CI(s) ↔ NH3(g) + HCI(g)

2SO2(g) + O2(g) ↔ 2SO3(g)

52

4

3

6

2

4

ONH

OHNOKc

32

1

2

2

3

HN

NHKc

11

3 HCINHKc

04

11

3

CINH

HCINHKc

12

2

2

2

3

OSO

SOKc

Equilibrium expression HETEROGENOUS rxn

CaCO3(s) ↔ CaO(g) + CO2(g)

03

1

2

1

CaCO

COCaOK c

12

1COCaOK c

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

152

1

3

1

2

1

523

OHHCCOOHCH

OHHCOOCCHK c

Equilibrium expression HOMOGENEOUS liquid rxn

Cu2+(aq) + 4NH3(aq) ↔ [Cu(NH3)4]

2+

43

12

2

43 )(

NHCu

NHCuK c

Reactant/product same phase

Reactant/product diff phase Solid and liq - conc no change (not included)

Page 11: IB Chemistry on Dynamic Equilibrium and Equilibrium Constant

Conc vs Time

How dynamic equilibrium is achieved in a closed system?

40 0

Rate forward = ½ breakdown = ½ x 40 = 20

Rate reverse = ¼ form = ¼ x 0 = 0

20 20

Rate forward = ½ breakdown = ½ x 20 = 10

Rate reverse = ¼ form = ¼ x 20 = 5

15 25

Rate forward = ½ breakdown = ½ x 15 = 8

Rate reverse = ¼ form = ¼ x 25 = 6

13 27

Rate forward = ½ breakdown = ½ x 13 = 7

Rate reverse = ¼ form = ¼ x 27 = 7

13 27

At dynamic Equilibrium Rate forward = Rate reverse Breakdown (7) = Formation (7)

At dynamic Equilibrium Conc reactant 13 /Product 27 constant

Rate vs Time

4/1

2/1

..tan..

..tan..

1

1 reversetconsrate

forwardtconsrate

K

K

213

27

tan

treac

productK c

24/1

2/1

1

1 K

KK c

or