reaction vessel remaining?

Question

For the following balanced chemical equation:

     2 Mg _(s)   +  O_{2 (g)}   →  2 MgO _(s)   

3.6 moles of Mg are put into a reaction container with 1.4 moles of O₂ gas. The reaction is run until all of the oxygen gas is used. How much Mg is remaining in the reaction vessel?

Answer 1

Since the question states that all O₂ is used up, this means that it is the limiting reagent. Use stoichiometry to convert mol O₂ to mol Mg.

1.4 mol O₂ x (2 mol Mg / 1 mol O₂) = 2.8 mol Mg

Out of 3.6 mol Mg, 2.8 mol reacts with 1.4 mol O₂.

mol Mg remaining = 3.6 - 2.8 = 0.8 mol Mg