Haber Process – Higher tier Quiz

1. The forward reaction in the Haber process is exothermic. Which change gives the largest increase in ammonia yield?

a) Increase temperature, decrease pressure
b) Decrease temperature, increase pressure
c) Increase both temperature and pressure
d) Decrease temperature, decrease pressure

2. At 450°C, only about 15% of the nitrogen and hydrogen convert to ammonia in one pass through the reactor. What is the main reason this low yield is acceptable industrially?

a) High temperatures always favour high yield
b) The forward reaction is instantaneous at 450°C
c) Unreacted gases are recycled, giving an overall yield of up to 98%
d) Nitrogen reacts much faster at high temperature

3. Which graph shape best represents how yield of ammonia changes as temperature increases?

a) Yield increases steadily with temperature
b) Yield decreases with temperature
c) Yield first increases then decreases
d) Yield stays constant at all temperatures

4. Pressure affects both the yield and cost of the Haber process. A plant operating at very high becomes uneconomic mainly because the equipment must be strong and able to withstand extreme forces.

5. The use of an iron catalyst in the Haber process:

a) increases the value of Kc
b) lowers activation energy and increases the rate
c) shifts equilibrium to the right
d) shifts equilibrium to the left

6. Why is a compromise temperature of about 450°C used?

a) It gives the highest possible yield
b) It gives a high yield but a very slow rate
c) It gives a reasonable rate and a reasonable yield
d) It allows the catalyst to produce more ammonia

7. The reaction N₂(g) + 3H₂(g) ⇌ 2NH₃(g) has 4 moles of gas on the left and 2 on the right. Which statement is true?

a) Increasing pressure increases ammonia yield
b) Increasing pressure decreases ammonia yield
c) Pressure has no effect on equilibrium position
d) Pressure only affects the catalyst

8. A student suggests lowering the temperature to 200°C to maximise yield. Why is this unsuitable for industry?

a) It produces too much ammonia too quickly
b) The rate of reaction would be far too slow
c) The reaction becomes endothermic at low temperatures
d) Nitrogen becomes unreactive below 300°C

9. The gas mixture leaving the reactor contains about 15% ammonia. How is ammonia removed from this equilibrium mixture?

a) Passing it back through the catalyst until it all reacts
b) Cooling and compressing so ammonia liquefies
c) Burning hydrogen to remove it
d) Using a membrane that only allows nitrogen to pass

10. A chemist claims that doubling the pressure from 200 atm to 400 atm will double the yield. Why is this incorrect?

a) Pressure has no effect beyond 150 atm
b) Yield increases, but not in direct proportion to pressure
c) The reaction becomes endothermic at high pressures
d) High pressure destroys the catalyst