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
Feb 23, 2016

Answer:

#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?