Question
"How do you determine the limiting reactant in a stoichiometry problem example?"
Answers
Answered by
GPT-4o mini
To determine the limiting reactant in a stoichiometry problem, you need to follow these steps:
1. **Write the Balanced Chemical Equation**: Start by writing the balanced equation for the chemical reaction. This will give you the mole ratios of the reactants involved.
Example: For the reaction between hydrogen and oxygen to form water, the balanced equation is:
\[
2H_2 + O_2 \rightarrow 2H_2O
\]
2. **Convert Amounts of Reactants to Moles**: If the quantities of the reactants are given in grams, you need to convert those amounts to moles using the molar masses of the substances.
Example:
- If you have 4 grams of \(H_2\):
\[
\text{Molar mass of } H_2 = 2.02 \, \text{g/mol}
\]
\[
\text{Moles of } H_2 = \frac{4 \, \text{g}}{2.02 \, \text{g/mol}} \approx 1.98 \, \text{moles}
\]
- If you have 2 grams of \(O_2\):
\[
\text{Molar mass of } O_2 = 32.00 \, \text{g/mol}
\]
\[
\text{Moles of } O_2 = \frac{2 \, \text{g}}{32.00 \, \text{g/mol}} \approx 0.0625 \, \text{moles}
\]
3. **Use the Mole Ratios from the Balanced Equation**: Compare the mole ratios of the reactants you calculated with the coefficients in the balanced equation to determine which reactant is limiting.
From the balanced equation, the mole ratio is:
\[
2 \, \text{moles of } H_2 : 1 \, \text{mole of } O_2
\]
4. **Calculate the Required Moles of Each Reactant**: For the amount of one reactant, calculate how much of the other reactant is needed based on the stoichiometric coefficients.
- From the calculated moles of \(H_2\) (1.98 moles):
Calculation needed moles of \(O_2\):
\[
\text{Required } O_2 = \frac{1.98 \, \text{moles } H_2}{2} = 0.99 \, \text{moles } O_2
\]
- You only have 0.0625 moles of \(O_2\), which is much less than the 0.99 moles required.
5. **Identify the Limiting Reactant**: The reactant that produces the least amount of product or is used up first in the reaction is the limiting reactant.
In this case, since you need 0.99 moles of \(O_2\) to react with 1.98 moles of \(H_2\) and you only have 0.0625 moles of \(O_2\), **\(O_2\) is the limiting reactant**.
By following these steps, you can determine the limiting reactant in any stoichiometry problem.
1. **Write the Balanced Chemical Equation**: Start by writing the balanced equation for the chemical reaction. This will give you the mole ratios of the reactants involved.
Example: For the reaction between hydrogen and oxygen to form water, the balanced equation is:
\[
2H_2 + O_2 \rightarrow 2H_2O
\]
2. **Convert Amounts of Reactants to Moles**: If the quantities of the reactants are given in grams, you need to convert those amounts to moles using the molar masses of the substances.
Example:
- If you have 4 grams of \(H_2\):
\[
\text{Molar mass of } H_2 = 2.02 \, \text{g/mol}
\]
\[
\text{Moles of } H_2 = \frac{4 \, \text{g}}{2.02 \, \text{g/mol}} \approx 1.98 \, \text{moles}
\]
- If you have 2 grams of \(O_2\):
\[
\text{Molar mass of } O_2 = 32.00 \, \text{g/mol}
\]
\[
\text{Moles of } O_2 = \frac{2 \, \text{g}}{32.00 \, \text{g/mol}} \approx 0.0625 \, \text{moles}
\]
3. **Use the Mole Ratios from the Balanced Equation**: Compare the mole ratios of the reactants you calculated with the coefficients in the balanced equation to determine which reactant is limiting.
From the balanced equation, the mole ratio is:
\[
2 \, \text{moles of } H_2 : 1 \, \text{mole of } O_2
\]
4. **Calculate the Required Moles of Each Reactant**: For the amount of one reactant, calculate how much of the other reactant is needed based on the stoichiometric coefficients.
- From the calculated moles of \(H_2\) (1.98 moles):
Calculation needed moles of \(O_2\):
\[
\text{Required } O_2 = \frac{1.98 \, \text{moles } H_2}{2} = 0.99 \, \text{moles } O_2
\]
- You only have 0.0625 moles of \(O_2\), which is much less than the 0.99 moles required.
5. **Identify the Limiting Reactant**: The reactant that produces the least amount of product or is used up first in the reaction is the limiting reactant.
In this case, since you need 0.99 moles of \(O_2\) to react with 1.98 moles of \(H_2\) and you only have 0.0625 moles of \(O_2\), **\(O_2\) is the limiting reactant**.
By following these steps, you can determine the limiting reactant in any stoichiometry problem.