Match each term to its description

Excess reactant

The excess reactant is the reactant that can produce more of the product. This means it is the substance that remains after a chemical reaction has completed.

Limiting reactant

The limiting reactant is the reactant that can produce a lesser amount of the product. It determines the maximum amount of product that can be formed from the given reactants.

Theoretical yield

The theoretical yield is the amount of product predicted to be produced by the given reactants.

By identifying the limiting reactant, you can calculate the theoretical yield based on stoichiometric relationships in the balanced chemical equation.

Understanding Excess Reactant

In a chemical reaction, the excess reactant is the substance that remains after the reaction has gone to completion. This occurs because it is present in a quantity greater than what is needed to completely react with the limiting reactant.

Key Concepts

1. Limiting Reactant: The substance that runs out first, thus determining the maximum amount of product that can be formed.

2. Stoichiometric Coefficients: The proportions of reactants and products in a balanced chemical equation, which need to be understood to identify the excess reactant.

Example Calculation

Consider the reaction between nitrogen gas ($\text{N}_2$) and hydrogen gas ($\text{H}_2$) to form ammonia ($\text{NH}_3$):

Let's say we have 5 moles of $\text{N}_2$ and 15 moles of $\text{H}_2$.

1. Determine the mole ratio from the balanced equation:

2. Calculate the moles of $\text{H}_2$ required for the available $\text{N}_2$:

3. Compare the available moles of $\text{H}_2$ with the required moles: Since 15 moles of $\text{H}_2$ are exactly what's needed for 5 moles of $\text{N}_2$, neither reactant would be in excess in this case. Let's modify it to illustrate.

4. If you had 6 moles of $\text{N}_2$:

Since only 15 moles of $\text{H}_2$ are available, it becomes the limiting reactant and $\text{N}_2$ is the excess reactant.

Example Calculation (continued)

4. The amount of the excess reactant remaining can be calculated:

Conclusion

Understanding limiting and excess reactants allows for efficient usage of materials and can help predict the quantities of products formed in a reaction. Properly performing these calculations is crucial in both academic and industrial chemical settings.

Understanding the Limiting Reactant

In a chemical reaction, the limiting reactant is the substance that is completely consumed first and thus determines the amount of product that can be formed. Reactions stop when the limiting reactant is used up, preventing further production of products.

Stoichiometry of the Reaction

To identify the limiting reactant, you need to use the stoichiometric coefficients from the balanced chemical equation. For example, consider the following reaction:

$2H_2 + O_2 \rightarrow 2H_2O$

Steps to Identify the Limiting Reactant

1. Write the balanced chemical equation for the reaction.
2. Convert all given reactant quantities (often in grams) to moles using their molar masses.
3. Use the stoichiometric coefficients from the balanced equation to determine the mole ratio required for the reaction.
4. Compare the mole ratio of the given reactants with the required mole ratio to identify the reactant that is limiting.

Example Calculation

Suppose we have 5 moles of $H_2$ and 2 moles of $O_2$. To find the limiting reactant:

1. Balanced Equation: $2H_2 + O_2 \rightarrow 2H_2O$

2. Mole Ratios from the Balanced Equation:

• $2$ moles of $H_2$ react with $1$ mole of $O_2$.

3. Determine the Theoretical Quantities Needed:

• For 5 moles of $H_2$: $\text{Required moles of } O_2 = \frac{5 \text{ moles } H_2 \times 1 \text{ mole } O_2}{2 \text{ moles } H_2} = 2.5 \text{ moles } O_2$

4. Compare Available Moles:

• We have only 2 moles of $O_2$, but 2.5 moles are required.

Therefore, $O_2$ is the limiting reactant because we do not have enough $O_2$ to completely react with the available $H_2$.

Key Points

• The limiting reactant runs out first, limiting the amount of product.
• Excess reactants are those that are left over after the reaction is complete.
• Identifying the limiting reactant is crucial for calculating the theoretical yield of the reaction.

By understanding and identifying the limiting reactant, chemists can predict the amounts of products formed and optimize the use of reactants in industrial processes.