Physical 1 Section 1 - Unit 6: Equilibria

Question 1

State how an increase in pressure would change the position of the equilibrium and the value of the equilibrium constant for this reaction (2 marks)

Answer 1

• Equilibrium position: displaced to the right

- Equilibrium constant: no change

Question 2

Explain the term homogeneous (1 mark)

Answer 2

• All reactants in the same phase or state

Question 3

Explain the term dynamic equilibrium (1 mark)

Answer 3

• Forward and backward reactions occur at the same rate

- So there is no change in the proportions of reactants and products

Question 4

Explain the term equilibrium (1 mark)

Answer 4

• Concentrations of reactants and products are constant
  OR
• Rates of forward and backward reactions equal

Question 5

What effect would increasing temperature have on the yield of ammonia? (5 marks)

Answer 5

• Equilibrium will shift towards the left
• To oppose this
• Move in the endothermic, backwards direction
• To decrease the temperature
• Giving a lower yield of ammonia

Question 6

State le Chatelier’s principle (1 mark)

Answer 6

• If any factor is changed which affects an equilibrium, the equilibrium will shift to counteract the change

Question 7

State the effect, if any, of a catalyst on the time taken to reach equilibrium (1 mark)

Answer 7

• Time decreases

Question 8

State the effect, if any, of a catalyst on the position of an equilibrium (1 mark)

Answer 8

• No effect

Question 9

Explain, in terms of the behaviour of particles, why a high operating pressure is used in industry (2 marks)

Answer 9

• The reaction gets to equilibrium faster
• Higher pressure leads to higher concentration of particles
• So more collisions in a given time

Question 10

State what the effect is of increasing pressure on the yield of methanol (5 mark)

Answer 10

• Equilibrium will shift to oppose this
• Move towards the side with fewer moles of gas to try to reduce the pressure
• Position of equilibrium will shift towards the right
• Because there are 3 moles of gas on the left but only 1 mole of gas on the right
• Giving a higher yield of methanol

Question 11

Explain the general effect of increasing pressure on the yield produced (3 marks)

Answer 11

• Equilibrium will shift to oppose this
• Move towards the side with fewer moles of gas to reduce the pressure
• Therefore reducing the yield produced

Question 12

State the equation for the Haber process (1 mark)

Answer 12

N2 + 3H2 ⇌ 2NH3

Question 13

State the temperature, pressure and catalyst needed for the Haber process (3 marks)

Answer 13

• Temperature: 450°C
• Pressure: 200 – 1000 atm
• Catalyst: Iron