# Question 5f174

Feb 19, 2015

The number of moles of hydrogen produced will mirror the number of moles of $Z n$ that react, or, from a different perspective, will be half the number of moles of $H C l$ that react.

The balanced chemical equation for this reaction is

$Z {n}_{\left(s\right)} + 2 H C {l}_{\left(a q\right)} \to Z n C {l}_{2 \left(a q\right)} + {H}_{2 \left(g\right)}$

Now look at the mole ratios you have between $Z n$, $H C l$, and ${H}_{2}$: 1 mole of $Z n$ needs 2 moles of $H C l$ to produce 1 mole of ${H}_{2}$.

All you have to do now is figure out exactly how many moles you have. This is done by using the molarity of the $H C l$ solution to calculate how many moles of $H C l$ you have, since you know that $Z n$ is in excess.

C = n/V => n_("HCl") = C * V = "0.40 M" * 400*10^(-3)"L" = "0.160 moles"#

Therefore, the number of ${H}_{2}$ moles will be

$\text{0.160 moles HCl" * ("1 mole H"_2)/("2 moles HCl") = "0.800 moles}$ ${H}_{2}$