Question

Two moles of magnesium (Mg) and five moles of oxygen (O2) are placed in a
reaction vessel. When magnesium is ignited, it reacts with oxygen. What is the limiting reactant in this experiment?
Mg + O2 → MgO (unbalanced)

Answer 1

Mg

Answer 2

2Mg + O2 -->2MgO

2 mol Mg x (O2/2Mg) = 1 mol O2 needed

5 mol O2 x (2Mg/O2) = 10 mol Mg needed

we only have 2 mol of Mg
we have 5 mol of oxygen

Because we need 10 mol of Mg for this reaction and only have 2, Mg i the limiting reagent.