Question

In the reaction 2 HgO --> 2 Hg + O2, how many moles of O2 are produced when 19.9 moles of HgO are decomposed?

Answer 1

You can see that in the reaction, 2 moles of HgO produces 1 mol of O2 and we need to find the number of needed moles of O2 that are decomposed by 19.9 moles of HgO. We can use a rule of three, like this:

$\begin{gathered} 2\text{ moles HgO }\to\text{ 1 mol O2} \\ 19.9\text{ moles HgO }\to\text{ ? mol O2} \end{gathered}$

The calculation would be:

$19.9\text{ moles HgO}\cdot\frac{1molO_2}{2\text{ moles HgO}}=9.95molesO_2.$

The answer is that 9.95 moles of oxygen are decomposed by 19.9 moles of HgO.