5.22 understand that nitrogen from air, and ydrogen from natural gas or the cracking of hydrocarbons, are used in the manufacture of ammonia

Ammonia is manufactured using hydrogen and nitrogen (as ammonia is NH₃). The equation for the reaction is...

N_{2 (g)}  + 3H_{2 (g)} ⇌  + 2NH_{3 (g)} (+heat)

Hydrogen is sourced from natural gas. Nitrogen is sourced from the air (as the air is 78% nitrogen).

The manufacture of ammonia with hydrogen and nitrogen is reversible, therefore, as soon as ammonia is made, it starts to turn back into nitrogen and hydrogen. This mean that not all of the nitrogen and hydrogen is converted to ammonia and not all ammonia is converted into nitrogen and hydrogen (because, as soon as nitrogen and hydrogen are produced, it starts to turn into ammonia). This means the reaction reached a dynamic equilibrium.