Question

How many moles of nitrogen gas (N2) are needed in order to produce 5 moles of an NH3?N2+3H2–> 2 NH3

Answer 1

Step 1 - Reading a chemical equation

In order to properly 'read' a chemical equation, we must know that the bigger numbers, those that come before the formulas of each susbtance, represent a quantity in moles.

The given chemical equation could be read thus as:

$N_2+3H_2\to2NH_3$

one mole of N2 react with 3 moles of H2 producing 2 moles of NH3

Step 2 - Finding how many moles of N2 are needed

Reading a chemical equation is like obtaining its recipe: we discover the proportion between the substances, and we can use it to predict how much we wll need if we 'change' the recipe.

Since we want to produce 5 moles of NH3, we can use this proportion:

one mole of N2 produces 2 moles of NH3

Therefore:

$\begin{gathered} 1\text{ mole of N2 produces ---- 2 moles of NH3} \\ x\text{ moles of N2 would produce -- 5 moles of NH3} \\ \\ x=\frac{5}{2}=2.5\text{ moles of N2} \end{gathered}$

We would need thus 2.5 moles of N2.