O-LevelChemistryRates of Reaction5070/21 · Oct/Nov 2023 · Q67 Marks

The equation for the Haber process used in the production of ammonia is shown. N₂ + 3H₂ ⇌ 2NH₃

(a)(i)The nitrogen for this process comes from the air. State the percentage by volume of nitrogen in clean, dry air.[1]
(a)(ii)State a source of hydrogen for the Haber process.[1]
(b)(i)The forward reaction in the Haber process is exothermic. Explain, in terms of bond making and bond breaking, why this reaction is exothermic.[2]
(b)(ii)The transfer of thermal energy in a chemical reaction is called the enthalpy change. Write the symbol for an enthalpy change. Include the sign for an exothermic enthalpy change.[1]
(c)(i)Aqueous ammonia is an alkali. Aqueous ammonia reacts with dilute nitric acid to form a salt. Name this salt.[1]
(c)(ii)Name the experimental technique used to make a solution of this salt from dilute nitric acid and aqueous ammonia.[1]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2023). The mark or mark type is shown in brackets.

[1] (a)(i) 78%
[1] (a)(ii) Methane
[1] (b)(i) bond breaking is endothermic / bond breaking needs energy
[1] (b)(i) AND bond making is exothermic / bond making gives energy out
[1] (b)(i) more energy is released than absorbed / less energy is absorbed than released
[1] (b)(ii) ΔH –
[1] (c)(i) ammonium nitrate
[1] (c)(ii) titration

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