Unit 3-Equilibria

Question 1

What does this symbol mean?

⇌

Answer 1

This means that it is a reversible reaction where the reactants form products, which react together to give the reactants back.

Question 2

Why can equilibrium only be reached in a closed system?

Answer 2

None of the reactants or products are lost.

In an open system, products (or reactants) are lost, therefore equilibrium cannot be established.

Question 3

Describe the concentrations of reactants and products at equilibrium.

Answer 3

At equilibrium, the concentration of reactant and products remain constant but NOT always equal.

Question 4

Describe the rates of the forward and reverse reactions at equilibrium.

Answer 4

They take place at equal rates.

Question 5

To maximise profits, chemists employ strategies to move the position of equilibrium to the left or the right?

Answer 5

To the right in favour of the products.

Question 6

Name a reaction condition which will affect the position of equilibrium.

Answer 6

1. the addition or removal of reactants or products
2. altering temperature
3. altering pressure

Question 7

What happens when a system at equilibrium is subjected to a change?

Answer 7

The system will adjust itself to counteract the applied change.

Question 8

What way will the equilibrium lie in the following reaction if:

More Fe³⁺(aq) is added

Fe³⁺(aq) + CNS^-(aq) ⇌ FeCNS²⁺(aq)

Answer 8

1. Equilibrium will shift to the right and make more products.

Question 9

What way will the equilibrium lie in the following reaction if:

1. More FeCNS²⁺(aq)

Fe³⁺(aq) + CNS^-(aq) ⇌ FeCNS²⁺(aq)

Answer 9

1. Equilibrium will shift to the left and make more reactants.

Question 10

In the Haber process the forward reaction is an exothermic reaction.

N₂(g) + 3H₂ ⇌ 2NH₃(g) ΔH_{<span>forward</span>} is negative

Which way will the equilbrium shift if the temperature is increased?

Answer 10

If the temperature is increased, then the equilibrium will shift to the left (the endothermic direction), to remove the extra heat added.

Question 11

In the Haber process the forward reaction is an exothermic reaction.

N₂(g) + 3H₂ ⇌ 2NH₃(g) ΔH_{<span>forward</span>} is negative

Which way will the equilbrium shift is the temperature is decreased?

Answer 11

If the temperature is decreased, then the equilibrium will shift to the right (the exothermic direction), to replace the heat removed.

Question 12

In the Haber process

N₂(g) + 3H₂(g) ⇌ 2NH₃(g)

Explain the change in the position of equilibrium when the pressure is increased.

Answer 12

An increase in pressure would move the equilibrium to the right since there are a smaller number of moles of gas products than reactants.

Question 13

In the Haber process

N₂(g) + 3H₂(g) ⇌ 2NH₃(g)

Explain the change in the position of equilibrium when the pressure is decreased.

Answer 13

A decrease in pressure would move the equilibrium to the left since there are a larger number of moles of gas reactants than gas.

Question 14

Why would changing pressure have no effect on the following reaction?

H₂(g) + I₂(g) ⇌​ 2HI(g)

Answer 14

Both sides of the reaction have two moles of gases, so changing the pressure does not favour either side of the equilibrium.

Question 15

What effect would adding a catalyst to a reversible reaction have on the equilibrium?

Answer 15

Adding catalyst has no effect on the position of equilibrium.

Allows equilibrium to be reached more quickly, or established at a lower temperature