# A 10*g mass of aluminum reacts with a 19*g mass of oxygen gas. Which is the reagent in deficiency?

$2 A l + \frac{3}{2} {O}_{2} \rightarrow A {l}_{2} {O}_{3}$
Moles of aluminum, (10*g)/(26.98*g*mol^(-1); versus moles of dioxygen, (19*g)/(32.00*g*mol^(-1). Given a calculator it should be easy to see the reagent in deficiency. Remember you have to account for the reaction's stoichiometry: 4 moles of aluminum require 3 moles of oxygen for reaction.