Chemistry Limiting and Excess Reactants

Question

I have a problem I think I have the answer to but I needed some validation.

I have Mg(s)+Cu(ClO3)2(Aq)—> Mg(ClO3)2(aq)+Cu(s)

given 24.76g Mg reacting with 70.33g Cu(ClO3)2

it appears this equation is already balanced. Upon doing calculations mole ratio is 1:1:1:1 and therefore there is NO limiting or Excess Reactant. Is this correct? Why or why not?

and then I need to calculate the mass of Excess that remains but if there isn’t one, I can’t calculate? Help!

Answer 1

The stoichiometry is 1:1:1:1 which means that if you don't have the same number of moles of each reactant, one will be in excess.

1) Find moles of Mg and moles of Cu(ClO₃)₂

2) Whichever is less in moles is the limiting reactant - this is only true for 1:1 stoichiometry. If the stoich ratio required was not one, you could take the ratio of the moles of the two reactants and compare it to the stoichiometric ratio.

3) The moles left of the excess reactant is moles of excess - moles of limiting reactant for 1:1

4) Convert back to grams of excess reactant by multiplying by the molar mass.

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