A limiting reactant or limiting reagent is the reactant that is completely consumed in a reaction. The reaction stops as soon as the limiting reactant is totally consumed.
Consider if 152 grams of ethane (C2H6) are reacted with 231 grams of oxygen gas,
2C2H6(g) + 7O2(g) → 4CO2(g) + 6H2O(g)
Since the quantities of reactants given is in mass, they have to be converted to moles using their respective molar mass. The coefficients of the balanced equation give the mole ratio in which the reactants combine. Also recall here that a limiting reactant is completely used up during the reaction 2 moles of C2H6 needs 7 moles of O2 compared this with the moles of each reactant obtained in step 1.