Thas is the famous Haber process.
The chemical equation of the reaction involved is:
[tex]N_2(g)+3H_2(g)[/tex] ⇄ [tex]2NH_3(g)+heat[/tex] <-------- answer
As you see it is an equillibrium reaction where 4 molecules of reactants form 2 molecules of product.
The balance is checked in this way
Reactants Products
# of atoms # of atoms
Element
N 2 2 * 1 = 2 => check
H 3*2 = 6 2 * 3 = 6 => check
The number of atoms of each element is the same on both sides, which is what balancing is about.
