Chemical Equilibium

Question 1

Dynamic equilibrium

Answer 1

State in a reversible system where the forward and backward reactions continue ate the same rate, resulting in no net charge in macroscopic properties of reactants and products

Conditions:
1. Closed system whereby no matter allowed to enter/leave
2. Temperature must remain constant
3. Reaction is reversible

Question 2

Reaction quotient (Q_c)

Answer 2

The ratio of the concentration of products to reactants raised to their stoichiometric ratio

Question 3

Equilibrium constant (K_c)

Answer 3

The reaction quotient of reaction when reaction is at equilibrium

only affected by temperature

Question 4

Rate equation of xA + yB ⇄ zC

Answer 4

Forward reaction: K_f[A]^x[B]^y

Backward reaction: K_b[C]^z

For gases: K_p = P_z^C/P_x^AP_y^B

Question 5

Relation of K_f and K_b

Answer 5

K_f = 1/K_b

K_c = K_f/K_b

Question 6

Size of K_c relative to POE

Answer 6

K_c is small: POE to the left, yield of forward reaction low

K_c is large: POE to the right, yield of forward reaction high

Question 7

Homogeneous equilibrium

Answer 7

Equilibrium system where all substances involved are in the same phase

Hence concentrations of pure liquids/solids constant at a given T

Question 8

Heterogeneous equilibrium

Answer 8

Equilibrium system where all substances involved are not in the same phase

Question 9

ΔG^θ relation to reaction spontaneity

Answer 9

ΔG^θ < 0: forward reaction spontaneous, rate of fwd rxn > bwd rxn

ΔG^θ > 0: forward reaction spontaneous, rate of bwd rxn > fwd rxn

Question 10

ΔG^θ equation

Answer 10

ΔG^θ = -RTlnK

where K is the equilibrium constant, K_c

Question 11

How does changing concentration affect POE?

Answer 11

• Concentration changes
• By LCP POE shifts left/right to partially offset increase/decrease in concentration of x
• By producing more y until equilibrium is reached

Question 12

How does changing partial pressure affect POE?

Answer 12

• Partial pressure changes
• By LCP POE shifts left/right to partially offset increase/decrease in partial pressure of x
• By producing more y until equilibrium is reached

Question 13

How does changing total pressure of system by adding inert gas affect POE?

Answer 13

• Total pressure of system increase/decrease
• By LCP, POE shifts left/right to partially offset change in pressure
• Favouring fwd/bwd rxn that produces more/less gas molecules
• Thus decreasing/increasing total number of gas molecules

Question 14

How does changing total volume of system affect POE?

Answer 14

• Total volume decrease/increase, partial pressure of each gas increase/decrease
• Since pressure is proportional to concentration
• Since concentration of all molecules increase
• All particles are closer together
• Increasing the frequency of effective collisions
• Hence reaction reaches equilibrium faster

Question 15

How does changing temperature system affect POE?

Answer 15

• By LCP, reaction counteracts increase/decrease in temperature
• By favouring the endo/exothermic fwd/bwd reaction
• To absorb/release heat,
• Hence POE shifts left/right, hence increasing/decrease yield of reaction
• When temperature increases, rate constant of fwd and bwd rxn both increase
• Hence reaction reaches equilibrium faster

Question 16

Haber Process Equation

Answer 16

3H_2(g) + N_2(g) ⇄ 2NH_3(g) ΔH^θ = -92 KJ mol_-1

Question 17

Haber Process R&Cw

Answer 17

Temperature: 450°C
Pressure: 200 atm (mid)
Catalyst: Finely divided iron with aluminium oxide
Misc: Continual removal of ammonia to increase yield by shifting POE left

Question 18

The Haber Compromise

Answer 18

• The forward reaction is exothermic but very slow
• Thus increasing the temperature would decrease yield of ammonia
• However since reaction is slow
• Temperature needs to be increased to increase rate of production