Final answer:
To determine the limiting reactant, balance the equation if necessary, calculate the mole ratio, determine the moles required for complete reaction from the balanced equation, and compare the mole amounts to identify which reactant is used up first. In this case, chromium (Cr) is the limiting reactant.
Step-by-step explanation:
To determine the limiting reactant in the given chemical reaction between chromium (Cr) and phosphoric acid (H₃PO₄), follow these steps:
Balance the chemical equation, if not already balanced. The given equation is already balanced: 2Cr + 2H₃PO₄ → 2CrPO₄ + 3H₂.
Calculate the mole ratio from the balanced equation between Cr and H₃PO₄, which is 1:1.
Determine how many moles of each reactant you would need to use up the other. For Cr, the conversion is 0.50 mol Cr → 0.50 mol H₃PO₄. For H₃PO₄, the conversion is 0.75 mol H₃PO₄ → 0.75 mol Cr.
Compare the moles of H₃PO₄ needed to react with the available moles of Cr. Since 0.50 mol of Cr would require 0.50 mol of H₃PO₄, and you have 0.75 mol of H₃PO₄, there is excess phosphoric acid.
Therefore, Cr is the limiting reactant because it will be used up first, while some amount of H₃PO₄ will remain unreacted.