Homogeneous equilibria

Homogeneous equilibria

• Chemical equilibria in which reactants and products are in the same phase

Kc =[C]c[D]d

[A]a[B]b

Equilibrium constant expressedin terms of molar concentrations

Kp =PC

cPDd

PAaPB

b

Equilibrium constant expressedin terms of gas partial pressures

Heterogeneous equilibria

• Chemical equilibria in which reactants and products are not in the same phase

Heterogeneous equilibria

• Chemical equilibria in which reactants and products are not in the same phase

• The concentrations of pure solids and pure liquids do not, and can not, change

• Solids and liquids are left out of the equilibrium constant expression

Kc = [Ag+]1[Cl-]1

Predicting reaction direction

K

QQ

Predicting reaction direction

• If Q < K, reaction moves spontaneously towards products until equilibrium point

• If Q > K, reaction moves spontaneously towards reactants until equilibrium point

• If reaction is at equilibrium, reaction stays at equilibrium

Predicting reaction direction

K

Q>KQ<K

Predicting reaction direction

2 NOCl(g) 2 NO(g) + Cl2(g) → ← If Kc = 4.4 x 10-4 at 500 K, determine the direction of the reactionif [NO] = .04 n/L, [Cl2] = .02 n/L and [NOCl] = 1.63 n/L

Q =[NO]2[Cl2]

[NOCl]2=

[.04]2[.02]

[1.63]2= 1.2 x 10-5

Q < K

Predicting reaction direction

2 NOCl(g) 2 NO(g) + Cl2(g) → ← If Kc = 4.4 x 10-4 at 500 K, determine the direction of the reactionif [NO] = .04 n/L, [Cl2] = .02 n/L and [NOCl] = 1.63 n/L

Q =[NO]2[Cl2]

[NOCl]2=

[.04]2[.02]

[1.63]2= 1.2 x 10-5

Q < K

Reaction will proceed spontaneously towards products until the equilibrium point is reached

Reaction atequilibrium

Reaction tendsto form products

Reaction tendsto form products

K

Q

Q

Q

KK

[C]c[D]d

Q = [A]a[B]b

aA + bB cC + dD → ←

K

Q

Q

Q

KK

aA + bB = cC + dD

aA + bB > cC + dD aA + bB < cC + dD

aA + bB cC + dD → ← [C]c[D]d

Q = [A]a[B]b

N2 + 3 H2 2 NH3→←

Calculating equilibrium concentrations

Suppose at a certain temperature you combined .5 n/L N2 and .8 n/L H2, and at equilibrium had produced .15 n/L NH3. What is the equilibrium constant for the reaction at this temperature?

N2 + 3 H2 2 NH3→←

Calculating equilibrium concentrations

N2 + 3 H2 2 NH3→←

Suppose at a certain temperature you combined .5 n/L N2 and .8 n/L H2, and at equilibrium had produced .15 n/L NH3. What is the equilibrium constant for the reaction at this temperature?

Initial concentration

Equilibrium concentration

H2N2 NH3

.5 .8

.15

N2 + 3 H2 2 NH3→←

Suppose at a certain temperature you combined .5 n/L N2 and .8 n/L H2, and at equilibrium had produced .15 n/L NH3. What is the equilibrium constant for the reaction at this temperature?

Initial concentration

Equilibrium concentration

H2N2 NH3

.5 .8

.15

0

N2 + 3 H2 2 NH3→←

Suppose at a certain temperature you combined .5 n/L N2 and .8 n/L H2, and at equilibrium had produced .15 n/L NH3. What is the equilibrium constant for the reaction at this temperature?

Initial concentration

Equilibrium concentration

H2N2 NH3

.5 .8

.15

0

Change in concentration +.15

N2 + 3 H2 2 NH3→←

Suppose at a certain temperature you combined .5 n/L N2 and .8 n/L H2, and at equilibrium had produced .15 n/L NH3. What is the equilibrium constant for the reaction at this temperature?

Initial concentration

Equilibrium concentration

H2N2 NH3

.5 .8

.15

0

Change in concentration +.15-.225

N2 + 3 H2 2 NH3→←

Suppose at a certain temperature you combined .5 n/L N2 and .8 n/L H2, and at equilibrium had produced .15 n/L NH3. What is the equilibrium constant for the reaction at this temperature?

Initial concentration

Equilibrium concentration

H2N2 NH3

.5 .8

.15

0

Change in concentration +.15-.225

.15 n/L NH3(3 n/L H2/2 n/L NH3)

N2 + 3 H2 2 NH3→←

Suppose at a certain temperature you combined .5 n/L N2 and .8 n/L H2, and at equilibrium had produced .15 n/L NH3. What is the equilibrium constant for the reaction at this temperature?

Initial concentration

Equilibrium concentration

H2N2 NH3

.5 .8

.15

0

Change in concentration +.15-.225-.075

N2 + 3 H2 2 NH3→←

Suppose at a certain temperature you combined .5 n/L N2 and .8 n/L H2, and at equilibrium had produced .15 n/L NH3. What is the equilibrium constant for the reaction at this temperature?

Initial concentration

Equilibrium concentration

H2N2 NH3

.5 .8

.15

0

Change in concentration +.15-.225-.075

.15 n/L NH3(1 n/L N2/2 n/L NH3)

N2 + 3 H2 2 NH3→←

Suppose at a certain temperature you combined .5 n/L N2 and .8 n/L H2, and at equilibrium had produced .15 n/L NH3. What is the equilibrium constant for the reaction at this temperature?

Initial concentration

Equilibrium concentration

H2N2 NH3

.5 .8

.15

0

Change in concentration +.15-.225-.075

.575.425

N2 + 3 H2 2 NH3→←

Suppose at a certain temperature you combined .5 n/L N2 and .8 n/L H2, and at equilibrium had produced .15 n/L NH3. What is the equilibrium constant for the reaction at this temperature?

Initial concentration

Equilibrium concentration

H2N2 NH3

.5 .8

.15

0

Change in concentration +.15-.225-.075

.575.425

EQUILIBRIUM TABLE

N2 + 3 H2 2 NH3→←

Suppose at a certain temperature you combined .5 n/L N2 and .8 n/L H2, and at equilibrium had produced .15 n/L NH3. What is the equilibrium constant for the reaction at this temperature?

Equilibrium concentration

H2N2 NH3

.15.575.425

FROM EQUILIBRIUM TABLE

N2 + 3 H2 2 NH3→←

Suppose at a certain temperature you combined .5 n/L N2 and .8 n/L H2, and at equilibrium had produced .15 n/L NH3. What is the equilibrium constant for the reaction at this temperature?

Equilibrium concentration

H2N2 NH3

.15.575.425

FROM EQUILIBRIUM TABLE

K =[NH3]2

[N2] [H2]3

N2 + 3 H2 2 NH3→←

Suppose at a certain temperature you combined .5 n/L N2 and .8 n/L H2, and at equilibrium had produced .15 n/L NH3. What is the equilibrium constant for the reaction at this temperature?

Equilibrium concentration

H2N2 NH3

.15.575.425

FROM EQUILIBRIUM TABLE

K =[NH3]2

[N2] [H2]3=

[.15]2

[.425][.575]3= .278