4.15 - Making ammonia in a reversible reaction

Sources of nitrogen and hydrogen

Ammonia has the formula $\ce{NH3}$: each molecule contains one nitrogen atom and three hydrogen atoms. The conventional Haber process uses these sources:

Air contains a large proportion of nitrogen. Natural gas, mainly methane, is processed to obtain hydrogen; it is not simply a supply of hydrogen gas.

Balancing ammonia formation

Nitrogen and hydrogen form ammonia in the forward reaction. In the reverse reaction, ammonia decomposes into nitrogen and hydrogen.

Check the atoms: each side has two nitrogen atoms and six hydrogen atoms. The coefficients therefore give a reacting ratio of 1 nitrogen molecule : 3 hydrogen molecules : 2 ammonia molecules. The (g) symbols show that all three substances are gases in the reaction mixture.

[DIAGRAM: asset_name: ammonia_reversible_reaction_overview: Formation of ammonia and dynamic equilibrium - diagram 1; asset_slug: 117_4_15_formation_of_ammonia_as_a_reversible_reaction_between_nitrogen_extracted_f_diagram1; file: 117_4_15_formation_of_ammonia_as_a_reversible_reaction_between_nitrogen_extracted_f_diagram1_imagegen_v1.png; recommended_method: deterministic_drawn; description: Exact monochrome teaching visual for Edexcel 4.15. It shows air as the source of N2(g), natural gas as the source of H2(g), both entering a closed reaction vessel, the balanced reversible equation N2(g) + 3H2(g) <=> 2NH3(g), forward and reverse arrows, and a dynamic equilibrium note: forward rate = reverse rate; amounts stay constant. It must not include Haber process condition values, catalyst, yield-shift predictions, ammonia removal, recycling, or fertiliser production. Deterministic drawing is required because formulae, arrows and labels must be exact.]