You calculate the moles of product that can be formed from each reactant. The reactant that gives the fewest moles of product is the limiting reactant.
Here’s how it works.
Methane burns in oxygen to give carbon dioxide and water according to the equation:
CH₄ + 2O₂ → CO₂ + 2H₂O
In one experiment, a mixture of 0.250 mol of methane was burned in 1.25 mol of oxygen in a sealed steel vessel. Identify the limiting reactant.
a. Calculate the amount of CO₂ that can be formed from the CH₄.
0.250 mol CH₄ ×
b. Calculate the amount of CO₂ that can be formed from the O₂.
1.25 mol O₂ ×
Since CH₄ gives fewer moles of CO₂, CH₄ is the limiting reactant.
Here is a video which discusses how to determine limiting reactants. video from: Noel Pauller