Pupil sheet · Reversible reactions and equilibrium
Ammonia and sulfuric acid — questions
Name ______________________ Date ____________
Try every question before you use a nudge. Write in full sentences where you are asked to explain.
1. state
Supplement. For the Haber process, state (a) the symbol equation, (b) the source of the nitrogen and of the hydrogen, (c) the typical temperature, pressure and catalyst.
(a) Equation
(b) Sources
(c) Conditions
Nudge (only if you are stuck): Ammonia is NH3; the catalyst is a metal.
2. state
Supplement. Match each part of the Contact process to the right answer.
Write the number of the matching option.
- 20 000 kPa (200 atm)
- burning sulfur or roasting sulfide ores
- 450 °C
- iron
- 200 kPa (2 atm)
- vanadium(V) oxide
- 1. Temperature: ______
- 2. Pressure: ______
- 3. Catalyst: ______
- 4. Where the sulfur dioxide comes from: ______
Nudge (only if you are stuck): The Contact process uses a much lower pressure than the Haber process.
3. interpret / calculate
Supplement. The table gives the percentage of ammonia at equilibrium at 450 °C. (a) What is the percentage at 200 atm? (b) By how many percentage points does it rise from 100 atm to 300 atm? (c) Explain the trend.
| Pressure / atm | 50 | 100 | 200 | 300 | 400 |
|---|---|---|---|---|---|
| Ammonia at equilibrium / % | 9 | 16 | 28 | 36 | 42 |
(a) Ammonia at 200 atm: ______________ unit ________
(b) Rise from 100 atm to 300 atm: ______________ unit ________
(c) Explain the trend.
Nudge (only if you are stuck): For (b), subtract the value at 100 atm from the value at 300 atm.
4. explain
Supplement. In the Haber process the forward reaction is exothermic. (a) What would a lower temperature than 450 °C do to the yield of ammonia? (b) Explain why a lower temperature is not used.
(a) Effect on the yield
(b) Why it is not used
Nudge (only if you are stuck): Think about the yield and the rate separately.
5. explain
Supplement. Explain why a high pressure gives more ammonia in the Haber process, and give two reasons why the pressure is not raised much above 200 atm.
Why a high pressure gives more ammonia
Two reasons not to go higher
Nudge (only if you are stuck): Count the gas molecules; then think about pipes and pumps.
6. explain
Supplement. In the Contact process, 2SO2(g) + O2(g) ⇌ 2SO3(g), a higher pressure would move the position of equilibrium to the right. (a) and (b): explain why only 200 kPa (2 atm) is used. (c) Explain why the plant runs at 450 °C with a vanadium(V) oxide catalyst.
(a) Why the yield is already enough
(b) Why a higher pressure is not worth it
(c) Why 450 °C and the catalyst
Nudge (only if you are stuck): How much sulfur trioxide is made already at 2 atm? For (c), think about the rate as well as the yield.
7. explain
Supplement. Ethanol is made from ethene and steam: C2H4(g) + H2O(g) ⇌ C2H5OH(g). The forward reaction is exothermic. The typical conditions are 300 °C, 6000 kPa (60 atm) and a phosphoric acid catalyst. Explain (a) why a high pressure is used, (b) why 300 °C is a compromise, (c) why the unreacted ethene is recycled.
(a) High pressure
(b) 300 °C
(c) Recycling
Nudge (only if you are stuck): Use the same reasoning as for the Haber process.