How are mole ratios used in chemical calculations?

In order to determine the mole ratio, we need to begin with a balanced chemical equation.

For this reaction the balanced chemical equation is
#N_2 + 3H_2 -> 2NH_3#

The mole ratios are determined using the coefficients of the substances in the balanced chemical equation.

#1 mol n_2 : 3 mol H_2 : 2 mol NH_3#

The mole ratios for each substance pair would be

#1 mol N_2 : 3 mol H_2#

#(1 mol N_2)/ (3 mol H_2)# or #(3 mol H_2)/ (1 mol N_2)#

#1 mol N_2 : 2 mol NH_3#

#(1 mol N_2)/ (2 mol NH_3)# or #(2 mol NH_3)/ (1 mol N_2)#

#3 mol H_2 : 2 mol NH_3#

#(3 mol H_2)/ (2 mol NH_3)# or #(2 mol NH_3)/ (3 mol H_2)#

Mole ratios are used as a means of comparison of substances in a balanced chemical equation in order to determine amounts.

Using the same reaction for ammonia
#N_2 + 3H_2 -> 2NH_3#

How many moles of Hydrogen gas are necessary to react with 5 moles of Nitrogen.

We can use conversion factors in a process called stoichiometry.

# 5 mol N_2 x (3 mol H_2)/(1 mol N_2) = 15 mol H_2#

Mole ratio provides a comparison to cancel units. In this case the moles of Nitrogen cancel and we determine the moles of Hydrogen.

I hope this was helpful.
SMARTERTEACHER