Iron catalyst N₂ + H₂ NH₃ Unreacted gases recycled Pressure gauge Reactor Fig. 1 shows an energy profile for a reaction used to make ammonia. A technician c...
Question 1 Report
Fig. 1 shows an energy profile for a reaction used to make ammonia. A technician compares the reaction with and without an iron catalyst. Table 1 gives the time needed to make a fixed mass of ammonia.
| Condition | Time to make 100 g ammonia / min |
|---|---|
| No catalyst | 92 |
| Iron catalyst | 31 |
(a) Name the energy labelled A on Fig. 1. [1]
(b) Give the effect of an iron catalyst on the rate of reaction. [1]
(c) Suggest how a catalyst changes the energy profile. [2]
The table below shows a school laboratory trial using marble granules and hydrochloric acid. Fig. 1 shows a balance used instead of a gas syringe. Carbon dioxide escapes, so the mass falls.
| Time / s | Mass of flask and contents / g |
|---|---|
| 0 | 156.24 |
| 30 | 155.72 |
| 60 | 155.39 |
| 90 | 155.22 |
| 120 | 155.22 |
(a) What mass of gas has been produced after 90 s? [1]
(b) Use Table 1 to state when the reaction has finished. [1]
(c) Give one reason why the balance method must not use a bung in the flask. [1]
(d) Suggest one safety precaution for using hydrochloric acid. [2]
Answer Details
Energy profile and catalyst
- (a) Energy A is the activation energy, the minimum energy needed for reacting particles to react successfully. [1]
- (b) An iron catalyst increases the rate of reaction, so ammonia is made faster. The data support this because 100 g takes 31 min with iron rather than 92 min without it. [1]
- (c) A catalyst provides an alternative reaction pathway with a lower activation energy. At the same temperature, more collisions then have sufficient energy to react. [2]
Mass-loss method
- (a) The mass of carbon dioxide produced after 90 s is:
\[156.24\text{ g}-155.22\text{ g}=\mathbf{1.02\text{ g}}\]
The lost mass is carbon dioxide that has escaped. [1] - (b) The reaction has finished at 120 s, when the mass becomes constant at 155.22 g. No further gas is being produced. [1]
- (c) The flask must not have a bung because the gas must be able to escape. If it were sealed, the measured mass would not decrease as carbon dioxide formed. [1]
- (d) Suitable precautions include wearing eye protection and wearing gloves. Acid spills should be rinsed with plenty of water. [2]
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