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?

1 Answer
anor277
Feb 23, 2016

Zn(s) + 2HCl(aq) rarr ZnCl_2(aq) + H_2(g).

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 mol of HCl(aq); 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?

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