The balanced equation for the reaction of gaseous nitrogen with hydrogen to form ammonia is:

$$ \text{N}_2\text{(g)} + 3\text{H}_2\text{(g)} \longrightarrow 2\text{NH}_3\text{(g)} $$

In this reaction, one molecule of nitrogen reacts with three molecules of hydrogen to produce two molecules of ammonia. This reaction is exothermic, meaning that it releases heat.