We are asked what is the limiting reactant and how many molecules of product can form.
Step 1. Balance the reaction.
A2 + B2 → AB3
A2 + B2 → 2 AB3
A2 + 3 B2 → 2 AB3
Step 2. Calculate product base on both reactants.
A2 → 3 molecules
1 molecule A2 : 2 molecules AB3
= 9 molecules AB3
The scene below represents a mixture of A2 (blue) and B2 (green) before they react to form AB3.
(a) What is the limiting reactant?
(b) How many molecules of product can form?