IB Chemistry Equilibrium constant, Kc and Reaction quotient, Qc.

17
Dynamic Equilibrium Closed system Reversible Forward Rate, K f Reverse Rate, K r 2NO 2 (g) N 2 O 4 (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 NO 2 Conc N 2 O 4 With time Conc NO 2 decrease - Forward rate decrease Conc N 2 O 4 increase - Backward rate increase 2NO 2 (g) N 2 O 4 (g) Forward rate Backward rate Forward Rate = Backward Rate Conc NO 2 and N 2 O 4 remain UNCHANGED/CONSTANT brown colourless

description

IB Chemistry Equilibrium constant, Kc and Reaction quotient, Qc.

Transcript of IB Chemistry Equilibrium constant, Kc and Reaction quotient, Qc.

Page 1: IB Chemistry Equilibrium constant, Kc and  Reaction quotient, Qc.

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 2: IB Chemistry Equilibrium constant, Kc and  Reaction quotient, Qc.

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

Click here to view simulation

Page 3: IB Chemistry Equilibrium constant, Kc and  Reaction quotient, Qc.

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

Page 4: IB Chemistry Equilibrium constant, Kc and  Reaction quotient, Qc.

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

reversetconsrate

forwardtconsrate

K

K

..tan..

..tan..

1

1

Page 5: IB Chemistry Equilibrium constant, Kc and  Reaction quotient, Qc.

Large Kc

• Position equilibrium shift to right • More products > reactants

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 reactants > products

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

Kc

• Position equilibrium lies slightly right • Reactants and products equal amount

Reaction completion

Product favoured Reactant favoured Reactant/Product equal

cK

Temp dependent

Extend of rxn

Not how fast

Page 6: IB Chemistry Equilibrium constant, Kc and  Reaction quotient, Qc.

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

Page 7: IB Chemistry Equilibrium constant, Kc and  Reaction quotient, Qc.

aA bB

2aA 2bB

bB aA

aA bB

aA bB

a

b

cA

BK

aA bB

Equilibrium Constant Kc Equilibrium Constant Kc

b

a

cB

AK

'

c

cK

K1'

inverse

X2 coefficient

2'

cc KK

coefficient

2

1

a

b

c

A

BK

21

21

'

ccc KKK 21'

a

b

cA

BK

a

b

cA

BK

a

b

cA

BK

2

2'

2

1

aA bB bB cC

a

b

ciA

BK

b

c

ciiB

CK

+ 2 reactions + aA cC

a

c

a

b

b

c

cA

C

A

B

B

CK

'

ciciic KKK '

Effect on Kc

Inverse Kc

Square Kc

Square root cK

Multiply both Kc

2

1

ciiK ciK

Page 8: IB Chemistry Equilibrium constant, Kc and  Reaction quotient, Qc.

N2(g) + O2(g) ↔ 2NO(g)

2NO(g) + O2(g) ↔ 2NO2(g)

19103.2 ciK

6103ciiK

2NO2(g) ↔ N2(g) + 2O2(g)

13

619

107

103103.2

c

c

ciicic

K

K

KKKN2(g) + 2O2(g) ↔ 2NO2(g)

13107 cK

12'

13

'

1042.1

107

11

c

c

c

K

KK

HF(ag) ↔ H+(aq) + F -(aq)

H2C2O4(ag) ↔ 2H+(aq) + C2O4

2 -(aq)

4108.6 ciK

6108.3 ciiK

2HF(ag) + C2O42- ↔ 2F -

(aq) + H2C2O4(aq)

2HF(ag) ↔ 2H+(aq) + 2F -(aq)

2H+(ag) + C2O4

2- ↔ H2C2O4(aq)

7242'106.4108.6 cic KK

5

6

''106.2

108.3

11

cii

cK

K

12.0106.2106.4 57

'''

c

ccc

K

KKK

Kc for diff rxn Adding 2 rxns

+

Inverse rxn

Adding 2 rxns

2HF(ag) + C2O42- ↔ 2F -

(aq) + H2C2O4(aq)

+

HF(ag) ↔ H+(aq) + F -(aq)

4108.6 ciK

x2 coefficient

H2C2O4(ag) ↔ 2H+(aq) + C2O4

2 -

Inverse rxn

6108.3 ciiK

2HF(ag) ↔ 2H+(aq) + 2F -

(aq)

2H+(ag) + C2O4

2- ↔ H2C2O4(aq)

Add 2 rxn

7'106.4 cK

5''106.2 cK+

Effect on Kc Effect on Kc

Inverse rxn Inverts expression

Doubling rxn coefficient Squares expression

Tripling rxn coefficient Cubes expression

Halving rxn coefficient Square root expression

Adding 2 reactions Multiplies 2 expression

cK

1

2

cK

3

cK

cK

ii

c

i

c KK

Square Kc

Invert Kc

Multiply Kc

1

2

3

N2(g) + 2O2(g) ↔ 2NO2(g)

Page 9: IB Chemistry Equilibrium constant, Kc and  Reaction quotient, Qc.

H2 + I2 ↔ 2HI

50cK

12

1

2

2

IH

HIK c

2HI ↔ H2 + I2

2

1

2

1

2'

HI

IHK c

02.050

11'

c

cK

K

2SO2 + O2 ↔ 2SO3

12

2

2

2

3

OSO

SOKc

200cK

SO2 + O2 ↔ SO3

1.14200'

cc KK

2

1

4SO2 + 2O2 ↔ 4SO3

40000

200

,

22'

c

cc

K

KK

N2(g) + 3H2(g) ↔ 2NH3(g)

32

1

2

2

3

HN

NHKc

Kc is 170 at 500K Determine if rxn is at equilibrium when conc are at: [N2] =1.50, [H2] = 1.00, [NH3] = 8.00

00.150.1

00.8

3

2

1

2

2

3

c

c

Q

HN

NHQ

• Rxn not at equilibrium

• Shift to right, favour product

• Qc must increase, till equal to Kc

IB Questions

Determine Kc for inversing rxn

inverse

Determine Kc for halving rxn

2

1

1

2

2

2

2

3

OSO

SOK c

halving

Determine Kc for doubling rxn

2SO2 + O2 ↔ 2SO3 doubling

12

2

2

2

3

OSO

SOKc

200cK

2

1

2

2

2

2

3

OSO

SOK c

2 1

3 4

170cK7.42cQ

cc KQ

Page 10: IB Chemistry Equilibrium constant, Kc and  Reaction quotient, Qc.

Kc and Qc

H2(g) + I2(g) ↔ 2HI(g)

cK

Constant at fixed Temp

12

1

2

2

IH

HIK c

At equilibrium

Independent of initial conc

Initial conc of H2 , I2 and HI

00.4cQ

12

1

2

2

IH

HIQc

4.461012.01014.1

1052.21212

22

cK 4.46cK

Expt Initial Conc H2

Initial Conc I2

Initial Conc HI

1 0.0500 0.0500 0.100

Initial conc of H2 , I2 and HI

Expt Initial Conc H2

Initial Conc I2

Initial Conc HI

1 2.40 x 10-2 1.38 x 10-2 0

Expt Equilibrium Conc H2

Equilibrium Conc I2

Equilibrium Conc HI

1 1.14 x 10-2 0.12 x 10-2 2.52 x 10-2

At equilibrium conc

Not at equilibrium

H2(g) + I2(g) ↔ 2HI(g)

00.4

050.0050.0

100.02

cQ

Predict the direction of rxn

Difference between

cQ

Conc of product/reactant at

equilibruim conc

Reaction quotient at particular time

Not at equilibrium conc

Varies NOT constant

Page 11: IB Chemistry Equilibrium constant, Kc and  Reaction quotient, Qc.

Kc and Qc

H2(g) + I2(g) ↔ 2HI(g)

12

1

2

2

IH

HIK c

4.461012.01014.1

1052.21212

22

cK 4.46cK

At equilibrium conc

cc KQ cc KQ cc KQ

Reaction at equilibrium

More product > reactant

Rxn shift left more reactant

cc KQ

cQ

Bring Qc down

More reactant > product

Rxn shift right → more product

Bring Qc up cQ

cc KQ

cQ

Expt Initial Conc H2

Initial Conc I2

Initial Conc HI

1 0.0500 0.0500 0.100

Initial conc of H2 , I2 and HI

12

1

2

2

IH

HIQc

00.4050.0050.0

100.02

cQ

cQ

Expt Initial Conc H2

Initial Conc I2

Initial Conc HI

1 0.0250 0.0350 0.300

Initial conc of H2 , I2 and HI

12

1

2

2

IH

HIQc

1030350.00250.0

300.02

cQ

Click here to view notes

Page 12: IB Chemistry Equilibrium constant, Kc and  Reaction quotient, Qc.

Kc from reaction stoichiometry

H2(g) + I2(g) ↔ 2HI(g)

4.46 sameK c

12

1

2

2

IH

HIK c

Kc = 46.4 ( 730K) At equilibrium 4 diff initial conc of H2 , I2 and HI

4.461012.01014.1

1052.21212

22

cKRxn 1

same

Qc = Kc - rxn at equilibrium, no side/shift occur Qc < Kc – rxn shift right, favour product Qc > Kc – rxn shift left, favour reactant

Rxn 2, 3, 4 diff initial conc

more products

H2(g) + I2(g) ↔ 2HI(g)

cQ

Rxn shift to right

Rxn shift to left more reactants

treac

productQc

tan

treac

productQc

tan

cQ

cc KQ cc KQ cc KQ

12

1

2

2

IH

HIKc

Page 13: IB Chemistry Equilibrium constant, Kc and  Reaction quotient, Qc.

Kc and Qc

H2(g) + I2(g) ↔ 2HI(g)

12

1

2

2

IH

HIK c

00.4cQ

12

1

2

2

IH

HIQc

4.461012.01014.1

1052.21212

22

cK 4.46cK

Expt Initial Conc H2

Initial Conc I2

Initial Conc HI

1 0.0500 0.0500 0.100

Initial conc of H2 , I2 and HI

At equilibrium conc

Not at equilibrium

H2(g) + I2(g) ↔ 2HI(g)

00.4

050.0050.0

100.02

cQ

cc KQ cc KQ

Reaction at equilibrium

More reactant > product

Rxn shift right → more product

Bring Qc up cQ

cQ

cc KQ

00.4cQ 4.46cK<

Page 14: IB Chemistry Equilibrium constant, Kc and  Reaction quotient, Qc.

Kc and Qc

H2(g) + I2(g) ↔ 2HI(g)

12

1

2

2

IH

HIK c

103cQ

12

1

2

2

IH

HIQc

4.461012.01014.1

1052.21212

22

cK 4.46cK

Initial conc of H2 , I2 and HI

At equilibrium conc

Not at equilibrium

H2(g) + I2(g) ↔ 2HI(g)

cc KQ cc KQ

Reaction at equilibrium

More product > reactant

Rxn shift left more reactant

cc KQ

cQ

Bring Qc down cQ

Expt Initial Conc H2

Initial Conc I2

Initial Conc HI

1 0.0250 0.0350 0.300

1030350.00250.0

300.02

cQ

103cQ 4.46cK>

Page 15: IB Chemistry Equilibrium constant, Kc and  Reaction quotient, Qc.

How dynamic equilibrium is shifted when H2 is added ?

• Add H2 , Qc decrease • Position equilibrium shift to right • Rate forward and reverse increase • New equilibrium conc achieved when Rate forward Kf = Rate reverse Kr • More product NH3 ,but Kc unchanged

N2(g) + 3H2(g) ↔ 2NH3(g) 07.4cK

Equilibrium disturbed H2 added. More reactant

At equilibrium Conc reactant/product no change

At new equilibrium Conc reactant/product no change

24.2cQ

Equilibrium Conc H2 = 0.82M Equilibrium Conc N2 = 0.20M Equilibrium Conc NH3 = 0.67M

32

1

2

2

3

HN

NHKc

31

2

82.020.0

67.0cK

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

32

1

2

2

3

HN

NHQc

31

2

00.120.0

67.0cQ

07.4cK

New Equilibrium Conc H2 = 0.90M New Equilibrium Conc N2 = 0.19M New Equilibrium Conc NH3 = 0.75M

31

2

90.019.0

75.0cK

32

1

2

2

3

HN

NHKc

07.4cK

Shift to the right - Increase product - New Conc achieve - Qc = Kc again

cc KQ

Page 16: IB Chemistry Equilibrium constant, Kc and  Reaction quotient, Qc.

How dynamic equilibrium is shifted when H2 is added ?

• Add H2 , Qc decrease • Position equilibrium shift to right • Rate forward and reverse increase • New equilibrium conc achieved when Rate forward Kf = Rate reverse Kr • More product NH3 ,but Kc unchanged

Rate forward Kf = Rate reverse Kr

N2(g) + 3H2(g) ↔ 2NH3(g) 07.4cK

07.4 cc KQ

Equilibrium disturbed H2 added. More reactant

cc KQ

Equilibrium shift to right Rate forward Kf > Rate reverse Kr

cQ

At equilibrium Conc reactant/product no change

At new equilibrium Conc reactant/product no change

Qc increase until Qc = Kc

cQ

Rate forward Kf = Rate reverse Kr

cc KQ

cc KQ cc KQ