How are mole ratios used in chemical calculations?

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Answer 1 · 2014-05-11T16:35:25

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

For this reaction the balanced chemical equation is
$N_{2} + 3 H_{2} \to 2 N H_{3}$ $N_2 + 3H_2 -> 2NH_3$

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

$1 m o l n_{2} : 3 m o l H_{2} : 2 m o l N H_{3}$ $1 mol n_2 : 3 mol H_2 : 2 mol NH_3$

The mole ratios for each substance pair would be

$1 m o l N_{2} : 3 m o l H_{2}$ $1 mol N_2 : 3 mol H_2$

$\frac{1 m o l N_{2}}{3 m o l H_{2}}$ $(1 mol N_2)/ (3 mol H_2)$ or $\frac{3 m o l H_{2}}{1 m o l N_{2}}$ $(3 mol H_2)/ (1 mol N_2)$

$1 m o l N_{2} : 2 m o l N H_{3}$ $1 mol N_2 : 2 mol NH_3$

$\frac{1 m o l N_{2}}{2 m o l N H_{3}}$ $(1 mol N_2)/ (2 mol NH_3)$ or $\frac{2 m o l N H_{3}}{1 m o l N_{2}}$ $(2 mol NH_3)/ (1 mol N_2)$

$3 m o l H_{2} : 2 m o l N H_{3}$ $3 mol H_2 : 2 mol NH_3$

$\frac{3 m o l H_{2}}{2 m o l N H_{3}}$ $(3 mol H_2)/ (2 mol NH_3)$ or $\frac{2 m o l N H_{3}}{3 m o l H_{2}}$ $(2 mol NH_3)/ (3 mol H_2)$

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
$N_{2} + 3 H_{2} \to 2 N H_{3}$ $N_2 + 3H_2 -> 2NH_3$

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.

$5 m o l N_{2} x \frac{3 m o l H_{2}}{1 m o l N_{2}} = 15 m o l H_{2}$ $5 mol N_2 x (3 mol H_2)/(1 mol N_2) = 15 mol H_2$

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