# How many moles of Zn will be needed to completely react with 0.4 moles of HCl in the reaction Zn + HCl -> ZnCl_2 + H_2?

Feb 23, 2016

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

$0.2$ moles of zinc metal are required for reaction with 0.4 moles of hydrochloric acid.

#### Explanation:

The equation above is stoichiometrically balanced. What does this mean? It means that for every reactant particle, there is a corresponding product particle. Stoichiometry is also practised in commerce: for every debit item (each charge made to an account), there must be a corresponding credit item (a deposit to made to another account). This principle of "rob Peter, and pay Paul" is fundamental to stoichiometry.

You started with $0.4$ $m o l$ of $H C l \left(a q\right)$; I could have started with 4 atoms, or 40 atoms, or 40 moles. By the stoichiometry of the reaction, each zinc particle requires 2 hydrochloric acid particles (i.e. each equivalent of zinc metal requires 2 hydrochloric acid particles). Thus $0.2$ mol of zinc metal were required.

Capisce?