Теоретичний вихід

What is a Theoretical Yield?

We've been studying stoichiometry. But so far, it's just been a lot of dimensional analysis. Why do even care? When we combine reactants, we start a chemical reaction. In theory, the reaction will yield the maximum amount of product. We call the maximum possible amount of product the theoretical yield. The only way to know the theoretical yield is to calculate it! How? Using stoichiometry!

How to Determine Theoretical Yield

The steps for determining the theoretical yield are...

• Balance the chemical equation.

• Determine the moles of each reactant.

• If we are told the mass, we need to use the molecular weight.

• If we are given the volume, we use density.

• If we have gases at STP, we can use the special conversion factor ($\frac{22.4L}{mol}$).

• Determine the limiting reagent. Convert moles of reactant to moles of product for each reactant. Remember, this involves using the mole ratio. The smaller quantity is the limiting reagent.

• Use the limiting reagent to calculate the mass or volume of the product. This is the theoretical yield!

The amount of product calculated from the limiting reagent is the theoretical yield. This is the maximum amount of product we can make. However, reactions do not always produce 100% of the expected theoretical yield. The reaction may not go to completion or some product may be lost when transferring material. The amount collected is the actual yield. The comparison of the actual and theoretical yields is the percent yield. It represents how experimental error and uncertainty affected our reaction.

Example Calcualtion

5.00 grams of solid sodium hydroxide $NaOH(s)$ reacts with 5.00 grams of liquid hydrogen chloride $HCl$, in a double-replacement reaction. The products are sodium chloride $NaCl$ and water. What is the theoretical yield for $NaCl$?

Balance the Chemical Equation:

$1NaOH(s) + 1HCl(l) \rightarrow 1NaCl(s) + 1H_2O(l)$

Determine the Moles of Each Reactant:

$5.00g\, NaOH \times \frac{1\, mol\, NaOH}{40g\, NaOH}=0.125mols\, NaOH$

$5.00g\, HCl \times \frac{1mol\, HCl}{36.0g\, HCl} =0.139mols\,HCl$

Determine Limiting Reagent:

$0.125mols\, NaOH \times \frac{1mol\, NaCl}{1mol\, NaOH}=0.125mols\, NaCl$

$0.139mols\,HCl \times \frac{1mol\, NaCl}{1mol\, HCl} =0.139mols\, NaCl$

Sodium hydroxide produces less sodium chloride. So, it's our limiting reagent.

Determine the Theoretical Yield of NaCl:

$0.125mols\, NaCl \times \frac{58.4g\, NaCl}{1mol\, NaCl}=7.3g\, NaCl$

(Video) Theoretical Yield: How To Calculate Theoretical Yield and Percent Yield

By The Organic Chemistry Tutor

This video demonstrates how to calculate theoretical yield through examples. To calculate theoretical yield, you need to balance the chemical equation first. Then, you need to find the limiting reagent. After that, you want to find the mole of the limiting reagent, which can be used to determine the ideal product amount based on the mole ratio between the products and the limiting reagent. Lastly, multiply the molecular weight of each product. This will give you the 100% yield, which is the theoretical yield.

Theoretical Yield: What is Theoretical Yield/How to Calculate it?

To calculate theoretical yield, you need to balance the chemical equation first. This is crucial for determining the limiting reagent. After finding the limiting reagent, you want to find the mole of the limiting reagent. You can use it to determine the ideal product amount based on the mole ratio between each product and the limiting reagent. Lastly, multiply the mole amount with the molecular weight of each product.