Stoichiometry of Limiting Reactants: Calculation Examples

📚 Quick Study Guide

• ⚖️ Stoichiometry is the study of the quantitative relationships or ratios between two or more substances when undergoing a physical change or chemical reaction.
• 🧪 A limiting reactant is the reactant that is completely consumed in a chemical reaction and limits the amount of product formed.
• ➕ The excess reactant is the reactant that is not completely consumed in a chemical reaction.
• ➗ To determine the limiting reactant:
  1. Calculate the moles of each reactant.
  2. Use the balanced chemical equation to find the mole ratio of reactants.
  3. Divide the moles of each reactant by its stoichiometric coefficient. The reactant with the smallest value is the limiting reactant.
• 📐 The theoretical yield is the maximum amount of product that can be formed from a given amount of limiting reactant.
• 💯 The percent yield is the actual yield divided by the theoretical yield, multiplied by 100%: $ \text{Percent Yield} = \frac{\text{Actual Yield}}{\text{Theoretical Yield}} \times 100$%

🧪 Practice Quiz

1. Question 1: In the reaction $2H_2 + O_2 \rightarrow 2H_2O$, if you have 4 moles of $H_2$ and 2 moles of $O_2$, which is the limiting reactant?
   1. $H_2$
   2. $O_2$
   3. $H_2O$
   4. Neither, they are in perfect stoichiometric amounts.
2. Question 2: For the reaction $N_2 + 3H_2 \rightarrow 2NH_3$, if you start with 6 moles of $H_2$, how many moles of $N_2$ are required to react completely with all the $H_2$?
   1. 1 mole
   2. 2 moles
   3. 3 moles
   4. 6 moles
3. Question 3: If 10.0 g of $Al$ react with 35.0 g of $Cl_2$ according to the equation $2Al + 3Cl_2 \rightarrow 2AlCl_3$, which is the limiting reactant? (Molar mass of $Al$ = 27.0 g/mol, Molar mass of $Cl_2$ = 71.0 g/mol)
   1. $Al$
   2. $Cl_2$
   3. $AlCl_3$
   4. Neither, they are in perfect stoichiometric amounts.
4. Question 4: Consider the reaction $CuO + H_2 \rightarrow Cu + H_2O$. If 79.5 g of $CuO$ reacts with 2.0 g of $H_2$, what is the limiting reactant? (Molar mass of $CuO$ = 79.5 g/mol, Molar mass of $H_2$ = 2.0 g/mol)
   1. $CuO$
   2. $H_2$
   3. $Cu$
   4. $H_2O$
5. Question 5: In a reaction where the theoretical yield is 25.0 g and the actual yield is 20.0 g, what is the percent yield?
   1. 125%
   2. 80%
   3. 20%
   4. 5%
6. Question 6: For the reaction $2SO_2(g) + O_2(g) \rightarrow 2SO_3(g)$, if you have 8.0 g of $SO_2$ and 2.0 g of $O_2$, which is the limiting reactant? (Molar mass of $SO_2$ = 64.0 g/mol, Molar mass of $O_2$ = 32.0 g/mol)
   1. $SO_2$
   2. $O_2$
   3. $SO_3$
   4. Neither, they are in perfect stoichiometric amounts.
7. Question 7: If 5.0 g of $H_2$ are allowed to react with 16.0 g of $O_2$ according to the reaction $2H_2 + O_2 \rightarrow 2H_2O$, how many grams of water are produced? (Molar mass of $H_2$ = 2.0 g/mol, Molar mass of $O_2$ = 32.0 g/mol, Molar mass of $H_2O$ = 18.0 g/mol)
   1. 9.0 g
   2. 18.0 g
   3. 22.5 g
   4. 36.0 g