Question

The balanced reaction equation for combustion of Mg is: 2 Mg + O2 --> 2 MgO.
In the reaction vessel you have 1.0 moles of Mg and 0.30 moles of O2. What is the limiting reactant? How many moles of MgO can you possibley make?

Answer 1

Here is a worked example of a simple stoichiometry problem. Follow the steps.
http://www.jiskha.com/science/chemistry/stoichiometry.html
Use the procedure twice, once for one reactant and next for the other reactant. This will give you two answers for moles CO2; the smaller one is the correct value to choose and the reactant giving that value is the limiting reagent.