Chapter 9- Chemical Equilibria

Question 1

What’s the Reaction Quotient, Q?

Answer 1

The reaction quotient (Q) is a function of the activities or concentrations of the chemical species involved in a chemical reaction

Question 2

Equation for reaction quotient

Answer 2

Qc= ([C]^c x [D]^d)/ ([A]^a x [B]^b)

Question 3

What is Q called at equilibrium?

Answer 3

K, the equilibrium constant

Question 4

How are ΔGº and K connected?

Answer 4

ΔGº = -RTlnK

Question 5

When does the equilibrium favour the products?

Answer 5

When ΔGº<0, K>1

Question 6

When does the equilibrium favour the reactants?

Answer 6

When ΔGº>0, K<1

Question 7

What’s Le Chatelier’s principle?

Answer 7

If an outside influence upsets an equilibrium, the system undergoes a change in a direction that counteracts the disturbing influence.

Question 8

What factors can upset an equilibrium?

Answer 8

Adding or removing reactants or products
Changing the pressure
Changing the temperature
Adding an inert gas
Adding a catalyst

Question 9

How does adding/ removing products/ reactants affect the equilibrium?

Answer 9

Equilibrium constant does not change, but the concentrations or partial pressures will change
Removing a product or adding more reactant pushes equilibrium further towards products
Removing a reactant or adding more product pushes equilibrium back towards reactants

Question 10

How does changing the pressure affect the equilibrium?

Answer 10

For a reaction that leads to an increase in the amount of gas, increasing pressure will push the equilibrium back towards reactants
For a reaction that leads to a decrease in the amount of gas, increasing pressure will push the equilibrium further towards products

Question 11

How does changing the temperature affect the equilibrium?

Answer 11

Equilibrium constant, concentrations or partial pressures will all change
The effect will depend upon whether 𝛥𝐻 > 0 or 𝛥𝐻< 0
If 𝛥𝐻> 0, then if temperature increases, then K will increase
If 𝛥𝐻 < 0, then if temperature increases, then K will decrease

Question 12

How does adding a catalyst affect the equilibrium?

Answer 12

Changes the rate of reaction but neither the equilibrium constant or the concentrations or partial pressures once equilibrium has been attained.

Question 13

Kc=

Answer 13

(([C]/𝑐∘)^𝑐 x ([D]/𝑐∘)^𝑑) / (([A]/𝑐∘)^𝑎 x ([B]/𝑐∘)^b)

Question 14

Kp=

Answer 14

((𝑝C/𝑝∘)^𝑐 x (𝑝D/𝑝∘)^𝑑) / ((𝑝A/𝑐∘)^𝑎 x (𝑝B/𝑐∘)^b)

Question 15

In Δ𝐺∘ = −𝑅𝑇 lnK, if we use 𝐾 = 𝐾𝑝, what is ΔG∘ measuring?

Answer 15

Δ𝐺∘ is the difference between the Gibbs energies of the products and reactants in their pure form at 1 bar.

Question 16

In Δ𝐺∘ = −𝑅𝑇 lnK, if we use 𝐾 = 𝐾c, what is ΔG∘ measuring?

Answer 16

Δ𝐺∘ is the difference between the Gibbs energies of the products and reactants at a concentration of 1 mol dm–3.