# In the equation N_2 + H_2 -> NH_3, what mass of ammonia gas can be produced from 12 mol of hydrogen gas?

Jan 5, 2016

12 mol of hydrogen produces 8 mol of ammonia, which then translates into 136.32 g. Round to significant figures and you get 140 g

#### Explanation:

First, you MUST balance the equation:
N_2 + 3 H_2 → 2 NH_3
This shows you that for every 3 moles of hydrogen, you can produce 2 moles of ammonia.

Then, you can calculate how many moles of ammonia are produced when 12 moles of hydrogen reacts. Keep in mind, you also need a certain amount of nitrogen gas, but that's not what the question is asking, so we can ignore it.

We write what we know from the balanced equation first, then an equal sign, then what the question is asking:

$\frac{3 m o l {H}_{2}}{2 m o l N {H}_{3}} = \frac{12 m o l {H}_{2}}{x m o l N {H}_{3}}$

Solve for "x" by cross multiplying

$12 \cdot 2 = 3 \cdot x$
$\frac{12 \cdot 2}{3} = x$

$8 = x$

Therefore, 12 moles of hydrogen makes 8 moles of ammonia.

Then you multiply by the molar mass of ammonia to find the mass:
$8 m o l N {H}_{3} \times \frac{17.04 g}{m o l} = 136.32 g$

You only have 2 significant figures in the question, so your last step is to round your answer to 2 significant figures.

Final answer: 140 g or $1.4 \times {10}^{2} g$