The diagram shows a school laboratory model of ammonia manufacture. Dry nitrogen and dry hydrogen are mixed in the box before being passed over heated iron ...
Question 1 Report
The diagram shows a school laboratory model of ammonia manufacture. Dry nitrogen and dry hydrogen are mixed in the box before being passed over heated iron wool. A student compares the volume of ammonia collected in equal times. Table 1 gives the results when the gas mixture has different nitrogen to hydrogen volume ratios. The gases in the box are measured at the same temperature and pressure.
| Nitrogen : hydrogen volume ratio | Ammonia collected in 5 min / cm3 |
|---|---|
| 1 : 2 | 32 |
| 1 : 3 | 46 |
| 1 : 4 | 44 |
(a) Complete the word equation: nitrogen + hydrogen ⇌ ______. [1]
(b) Use Table 1 to give the ratio that produced most ammonia. [1]
(c) Name the element in the iron wool that acts as a catalyst. [1]
(d) Suggest why the gases are dried before entering the apparatus. [1]
A student investigates the effect of pressure on an equilibrium mixture for ammonia production using a sealed demonstration chamber. Fig. 1 shows a movable piston compressing nitrogen and hydrogen over an iron catalyst. The chamber is allowed to reach equilibrium before each sample is analysed. Table 1 shows the percentage of ammonia in the final gas mixture. Temperature is kept at 450 °C throughout.
| Pressure / atm | Ammonia in equilibrium mixture / % |
|---|---|
| 80 | 14 |
| 150 | 23 |
| 250 | 31 |
(a) Complete the balanced equation: N₂ + 3H₂ ⇌ ______. [1]
(b) Use Table 1 to state the effect of increasing pressure on ammonia percentage. [1]
(c) Explain this effect using the number of gas molecules in the equation. [2]
(d) Give one disadvantage of using very high pressure in an industrial plant. [1]
Answer Details
Ammonia manufacture model
(a) nitrogen + hydrogen \(\rightleftharpoons\) ammonia. [1]
(b) The ratio producing the most ammonia is 1 volume nitrogen : 3 volumes hydrogen, giving 46 cm3 in 5 minutes. [1]
(c) The catalyst element in the iron wool is iron. [1]
(d) The gases are dried to prevent water contaminating the product or affecting the reaction. [1]
Effect of pressure
(a) \(\text{N}_2+3\text{H}_2\rightleftharpoons\)\(2\text{NH}_3\). [1]
(b) The ammonia percentage increases as pressure increases. [1]
(c) The left side contains 4 gas molecules, or moles of gas [1], while the right side contains only 2. Higher pressure favours the side with fewer gas molecules, so it favours ammonia. [1]
(d) Very high pressure requires expensive compression and high energy use, or stronger costly equipment. [1]
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