Equilibria RSC starters for 10

Equilibria

This question is about the equilibrium established between hydrogen, iodine and hydrogen iodide; H₂ + I₂ ⇌ 2 HI

Multiple Select

This question is about the equilibrium established between hydrogen, iodine and hydrogen iodide; H₂ + I₂ ⇌ 2 HI

The rate of the forward and backward reaction must be the same

• True

• False

Multiple Select

This question is about the equilibrium established between hydrogen, iodine and hydrogen iodide; H₂ + I₂ ⇌ 2 HI

The concentration of the reactants and products is the same

• True

• False

Multiple Select

This question is about the equilibrium established between hydrogen, iodine and hydrogen iodide; H₂ + I₂ ⇌ 2 HI

The equilibrium must have been established by reacting hydrogen with iodine

• True

• False

Multiple Select

This question is about the equilibrium established between hydrogen, iodine and hydrogen iodide; H₂ + I₂ ⇌ 2 HI

The system must be sealed

• True

• False

Multiple Select

This question is about the equilibrium established between hydrogen, iodine and hydrogen iodide; H₂ + I₂ ⇌ 2 HI

Iodine is purple in colour. Hydrogen and hydrogen iodide are colourless. Therefore as the iodine is used up, the colour of the system will gradually fade.

• True

• False

Multiple Select

This question is about the equilibrium established between hydrogen, iodine and hydrogen iodide; H₂ + I₂ ⇌ 2 HI

The pressure of the system will remain constant

• True

• False

Open Ended

Le Châtelier’s principle states that if a system at equilibrium is disturbed, the equilibrium moves in the direction that tends to minimise the disturbance. Use Châtelier’s principle to suggest two disturbances that can be made to each of the equilibria below to bring about the desired changes;

Cl₂(aq) + H₂O(l) ⇌ HClO(aq) + HCl(aq)

Two disturbances which would result in a decrease in the concentration of chlorine are

Cl₂(aq) + H₂O(l) ⇌ HClO(aq) + HCl(aq)

Possible disturbances which would result in a decrease in the concentration of chlorine are removal of either of the products from the system or addition of water to the system. (2 marks for any two

Open Ended

Le Châtelier’s principle states that if a system at equilibrium is disturbed, the equilibrium moves in the direction that tends to minimise the disturbance. Use Châtelier’s principle to suggest two disturbances that can be made to each of the equilibria below to bring about the desired changes;

4 HCl + O₂ ⇌ 2 Cl₂ + 2 H₂O ∆H –ive Two disturbances which would result in an increase in the concentration of chlorine are

4 HCl + O₂ ⇌ 2 Cl₂ + 2 H₂O ∆H –ive

Possible disturbances which would result in an increase in the concentration of chlorine are an increase in the concentration of either of the reactants, removal of water from the system or cooling the system. (2 marks for any two)

Open Ended

Le Châtelier’s principle states that if a system at equilibrium is disturbed, the equilibrium moves in the direction that tends to minimise the disturbance. Use Châtelier’s principle to suggest two disturbances that can be made to each of the equilibria below to bring about the desired changes;

PCl₅(g) ⇌ PCl₃(g) + Cl₂(g) ∆H +ive

Two disturbances which could be made without changing the amount of reagents or products in the system which would result in a shift of the equilibrium to the right are;

PCl₅(g) ⇌ PCl₃(g) + Cl₂(g) ∆H +ive

Two disturbances which could be made without changing the amount of reagents or products in the system which would result in a shift of the equilibrium to the right are increasing the temperature of the system or lowering the pressure of the system. (2 marks for any two)

Open Ended

Le Châtelier’s principle states that if a system at equilibrium is disturbed, the equilibrium moves in the direction that tends to minimise the disturbance. Use Châtelier’s principle to suggest two disturbances that can be made to each of the equilibria below to bring about the desired changes;

CH₂=CH₂(g) + H₂O(g) ⇌ CH₃CH₂OH(g) ∆H –46 kJ mol^–1

Two disturbances which would result in an increase in the percentage yield of ethanol are;

 CH₂=CH₂(g) + H₂O(g) ⇌ CH₃CH₂OH(g) ∆H –46 kJ mol^–1

Two disturbances which would result in an increase in the percentage yield of ethanol are a lowering of the temperature of the system or a increase in the pressure of the system. (2 marks for any two)

Open Ended

Le Châtelier’s principle states that if a system at equilibrium is disturbed, the equilibrium moves in the direction that tends to minimise the disturbance. Use Châtelier’s principle to suggest two disturbances that can be made to each of the equilibria below to bring about the desired changes;

HCOOH + CH₃OH ⇌ HCOOCH₃ + H₂O

∆H 0 kJ mol^–1

Two disturbances which would result in no change in the position of the equilibrium are;

HCOOH + CH₃OH ⇌ HCOOCH₃ + H₂O

∆H 0 kJ mol^–1

Two disturbances which would result in no change in the position of the equilibrium are a change in system temperature or addition of a catalyst. (2 marks for any two)

Multiple Select

Decide which set of conditions would result in the highest yield of the desired product for each of the equilibria

Production of hydrogen iodide

H₂(g) + I₂(g) ⇌ 2 HI(g) ∆H +53 kJ mol^–1

• Low termperature

• High temperature

• Low pressure

• High pressure

Production of hydrogen iodide, Conditions : high temperature and pressure has no effect

H₂(g) + I₂(g) ⇌ 2 HI(g) ∆H +53 kJ mol^–1

Multiple Select

Decide which set of conditions would result in the highest yield of the desired product for each of the equilibria

Making hydrogen

CH₄(g) + H₂O(g) ⇌ 3 H₂(g) + CO(g) ∆H +206 kJ mol^–1

• Low termperature

• High temperature

• Low pressure

• High pressure

Making hydrogen, Conditions: high temperature and low pressure

CH₄(g) + H₂O(g) ⇌ 3 H₂(g) + CO(g) ∆H +206 kJ mol^–1

Multiple Select

Decide which set of conditions would result in the highest yield of the desired product for each of the equilibria

Production of methanol

CO(g) + 2 H₂(g) ⇌ CH₃OH(g) ∆H –91 kJ mol^–1

• Low termperature

• High temperature

• Low pressure

• High pressure

Production of methanol, Conditions: low temperature and high pressure

CO(g) + 2 H₂(g) ⇌ CH₃OH(g) ∆H –91 kJ mol^–1

Open Ended

Another industrial process involving a reversible reaction is the production of sulphuric acid in the Contact Process. The first stage of the process is shown below;

2 SO₂(g) + O₂(g) ⇌ 2 SO₃(g) ∆H –196 kJ mol^–1

(a) i. Use Le Châtelier’s principle to explain why, at a given pressure, the percentage yield of sulfur trioxide increases with a lowering of the overall temperature. (3 marks)

2 SO₂(g) + O₂(g) ⇌ 2 SO₃(g) ∆H –196 kJ mol^–1

(a) i. Use Le Châtelier’s principle to explain why, at a given pressure, the percentage yield of sulfur trioxide increases with a lowering of the overall temperature. (3 marks)

ANSWER

The reaction is exothermic in the forward direction (1 mark). Therefore lowering the temperature of the system shifts the equilibrium in favour of the forward, exothermic reaction (1 mark) to return the temperature to its original value (1 mark). Therefore the percentage yield of sulfur trioxide is increased.

Open Ended

Another industrial process involving a reversible reaction is the production of sulphuric acid in the Contact Process. The first stage of the process is shown below;

2 SO₂(g) + O₂(g) ⇌ 2 SO₃(g) ∆H –196 kJ mol^–1

To increase the rate of the reaction, a vanadium pentoxide catalyst is used. Explain what effect this has on the overall percentage yield of sulfur trioxide. (2marks)

2 SO₂(g) + O₂(g) ⇌ 2 SO₃(g) ∆H –196 kJ mol^–1

To increase the rate of the reaction, a vanadium pentoxide catalyst is used. Explain what effect this has on the overall percentage yield of sulfur trioxide. (2marks)

ANSWER

Addition of a catalyst has no effect on the position of the equilibrium and therefore does not affect the overall yield (1 mark). This is because the catalyst speeds up the rate of both the forward and reverse reaction equally (1 mark).

Open Ended

Another industrial process involving a reversible reaction is the production of sulphuric acid in the Contact Process. The first stage of the process is shown below;

2 SO₂(g) + O₂(g) ⇌ 2 SO₃(g) ∆H –196 kJ mol^–1

The reaction is run at pressures close to atmospheric pressure. Use Le Châtelier’s principle to explain why this choice of pressure is unexpected and give a possible explanation for why it is chosen. (3marks)

2 SO₂(g) + O₂(g) ⇌ 2 SO₃(g) ∆H –196 kJ mol^–1

The reaction is run at pressures close to atmospheric pressure. Use Le Châtelier’s principle to explain why this choice of pressure is unexpected and give a possible explanation for why it is chosen. (3marks)

ANSWER

The reaction is run at pressures close to atmospheric pressure. Use Le Châtelier’s principle to explain why this choice of pressure is unexpected and give a possible explanation for why it is chosen. (3marks)