Ammonium nitrate, $$\(\mathrm{NH}_{4} \mathrm{NO}_{3}\)$$, is used in the manufacture of fertilisers and explosives. It is produced on a large scale using only methane, water and air. The process has four stages. The first two reactions in Stage 1 involve the production of hydrogen. At temperature $$\(T_{1}\)$$, methane reacts with excess steam to give hydrogen. $$\[ \mathrm{CH}_{4}(\mathrm{~g})+\mathrm{H}_{2} \mathrm{O}(\mathrm{g}) \rightleftharpoons 3 \mathrm{H}_{2}(\mathrm{~g})+\mathrm{CO}(\mathrm{g}) \quad \Delta H=+206 \mathrm{~kJ} \mathrm{~mol}^{-1} \]$$ At a different temperature, $$\(T_{2}\)$$, the carbon monoxide reacts with more steam. $$\[ \mathrm{CO}(\mathrm{g})+\mathrm{H}_{2} \mathrm{O}(\mathrm{g}) \rightleftharpoons \mathrm{H}_{2}(\mathrm{~g})+\mathrm{CO}_{2}(\mathrm{~g}) \quad \Delta H=-42 \mathrm{kJmol}^{-1} \]$$ Give the reason why excess steam is used in the first reaction. (1)

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