O-LevelChemistryRates of Reaction5070/21 · May/June 2016 · Q47 Marks

Ammonia is manufactured by the reaction between hydrogen and nitrogen in the Haber process.

(a)State the conditions used in the Haber process. temperature pressure catalyst[2]
(b)Describe and explain the effect of increasing the pressure on the rate of this reaction.[2]
(c)Explain how a catalyst speeds up the rate of a chemical reaction.[1]
(d)Ammonia is used to make fertilisers. The table gives some information about two fertilisers made from ammonia. | fertiliser | formula | relative formula mass (Mr) | |---|---|---| | ammonium nitrate | NH4NO3 | 80 | | urea | (NH2)2CO | 60 | Use the data in the table to show that urea contains a greater percentage by mass of nitrogen than ammonium nitrate.[2]

Mark scheme

Marking points from the official mark scheme (May/June 2016). The mark or mark type is shown in brackets.

[2] All three conditions correct (2 marks) Two correct conditions (1 mark) • Temperature: 350 to 500 °C • Pressure: 150 to 1000 atmospheres • Catalyst: iron
[2] Rate of reaction increases AND particles closer together/more particles per unit volume/more crowded particles (1) More collisions per second/increased collision frequency/collisions more often (1)
[1] Lowers the activation energy (1)
[2] Percentage of N in ammonium nitrate = 35% (1) Percentage of N in urea = 47% (1) OR Both formulae contain two nitrogen atoms (1) Urea has a lower relative formula mass (1)

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