Topic 10 Equilibrium 1

Question 1

What are the 2 conditions for dynamic equilibrium to be established?

Answer 1

• The reaction must be reversible.
• The reaction mixture must be in a closed container.

Question 2

What are 3 features of a system in dynamic equilibrium?

Answer 2

• Both the forward & backward reactions are continuously occurring.
• The rate of the forward reaction the rate of the backwards reaction.
• The concentrations of reactants & products remain constant.

Question 3

4 factors that may affect equilibrium:

Answer 3

• Concentration of a component.
• Pressure of the system.
• Temperature of the system.
• Addition of a catalyst.

Question 4

If we increase the concentration of one of the reactants in an equilibrium…

Answer 4

…equilibrium shifts right to favour the products.

Question 5

How can we change the pressure of a system in equilibrium?

Answer 5

Using a gas syringe, push the plunger in/pull it out.

Question 6

Effect of changing the pressure on an equilibrium system

Answer 6

Can be increased by adding more moles of a reactant in the same volume. Only applies to reactions involving gases. An increase in pressure shifts the position of equilibrium to the side with fewer gas moles.

Question 7

Effect of a change in temperature on the equilibrium

Answer 7

If the temperature of an equilibrium is raised, the rates of both the forward and backward reactions increase, however, the increase in the rate of the endothermic reaction will be greater, thus an increase in temperature shifts the position of equilibrium in the direction of the endothermic reaction.

Question 8

Effect of addition of a catalyst

Answer 8

Increases the rate of the forward & backward reactions to the same extent. Position of equilibrium is unchanged, but the time taken to reach equilibrium is reduced.

Question 9

Homogenous system

Answer 9

A system in which all components are in the same phase.

Question 10

Heterogeneous system

Answer 10

A system where at least 2 different phases are present.

Question 11

aA + bB <–> cC + dD
Equilibrium law

Answer 11

Kc = [C]^c[D]^d / [A]^a [B]^b

Question 12

For the reaction: H2(g) + I2(g) <–> 2HI (g)
Kc= [HI(g)]^2/[H2(g)][I2(g)] = 50
What is Kc for the reverse reaction?
And what is Kc for the reaction ion which only 1 HI(g) is produced?

Answer 12

K’c= [H2(g)][I2(g)] / [HI(g)]^2 = 0.02
And for the reaction: 1/2H2(g) + 1/2I2(g) <–> HI (g)
K’‘c = [HI(g)]/[H2(g)]^1/2[I2(g)]^1/2 = root 50 = 7.07

Question 13

Kc = [N2O4(g)]/[NO2(g)]
Use Kc to predict the effect of increasing the concentration of NO2(g).

Answer 13

The value of the denominator increases, so the value of [N2O4(g)]/[NO2(g)]is less than Kc.
The value of N2O4(g) must increases in order to restore Kc, so equilibrium shifts right, so that Kc is maintained.

Question 14

Compromise conditions for the Haber process

Answer 14

Iron, 450°C & 250 atm.

Question 15

The contact process: SO2(g) + 1/2O2(g) <–> SO3(g)

Answer 15

450°C (faster rate, improves the catalyst effectivity, but the forward reaction is exothermic). 2 atm (increases the yield).

Question 16

Why are catalysts used in industrial processes involving equilibria?

Answer 16

• Lowers the activation energy.
• Increases yield of product in the same amount of time.
• Increases the rate at which the reaction moves towards equilibrium.
• It allows milder conditions to be used, lowering the cost.

Question 17

Why might the product be removed before its maximum concentration is reached?

Answer 17

• The time taken to reach equilibrium may be too long.
• Unreacted reactants may be recycled.
• Removal of the product decreases the rate of the backward reaction, by shifting the position of equilibrium right.

Question 18

Disadvantage of using a heterogeneous catalyst to speed up the rate:

Answer 18

The rate is limited when all the reaction sites on the catalyst are occupied.

Question 19

Con of separating funnels.

Answer 19

Not suitable for industrial processes.

Question 20

Characteristic of all reactions in equilibrium (, so not necessarily dynamic equilibrium):

Answer 20

The concentration of all reactants & products is constant. The rate of the forward reaction is equal to the rate of the backwards reaction.

Question 21

When showing concentration over time on a graph for all the components of an equilibrium mixture…

Answer 21

… draw the lines as curves.