Ammonia formula is wrong.

The Chemical for Ammonia is NH3 Not N2H Your formula in the game should be 1 Nitrogen to 3 hydrogen. 3 times as much hydrogen as Nitrogen. You have it more hydrogen than nitrogen. You have N2H not NH3. Now with that said, The industrial process is not that simple.
Industrial Process: Ammonia can be produced from coal through a gasification process, where coal is converted into synthesis gas (H2, CO, CO2) and then reacted with nitrogen. But for simplification in the game, A chemical plant should use one part Nitrogen to 3 parts hydrogen, not 2 parts nitrogen to 1 part hydrogen.
Another option that is more environmentally friendly is a method using small droplets of water and nitrogen from the air to produce ammonia. (NH3)

Volume in CoI is measured in weight, Hydrogen is a little over 1 and Nitrogen is about 14. So you are correct, it is still wrong.. but you would get about 14 Units of Nitrogen for every 3 units of Hydrogen. A gamified number for 2 nitrogen for 1 hydrogen is reasonable. If you go by volume the amount of space hydrogen would take would not be fun., as the ratio space for equal amount of hydrogen for 1 unit of nitrogen would 1b 1200x times as much space.
I think this was a game balance choice.