how to find theoretical yield

Percent Yield

Percent yield refers to the percent ratio of actual yield to the theoretical yield. In chemistry, yield is a measure of the quantity of moles of a product formed in relation to the reactant consumed, obtained in a chemical reaction, usually expressed as a percentage. The amount of product actually made compared with the maximum calculated yield is called the percentage yield. Let us understand the percent yield formula using solved examples.

What is Percent Yield?

In chemistry, percent yield is the percent ratio of the weight of the product obtained to the theoretical yield. We calculate the percent yield by dividing the experimental yield by the theoretical yield and multiplying the result by 100 to express the final answer in %. Generally, the value of percent yield is lower than 100%, since the actual yield obtained after the reaction is often less than the theoretical value. This can be because of an incomplete reaction.

Percent yield can also be greater than 100%, meaning that more sample was recovered from the reaction than the initially predicted yield. Percent yield is always positive.

Percentage Yield Example

Let us see the decomposition reaction of magnesium oxide to understand the concept of percent yield better.

MgCO\(_3\) → MgO + CO\(_2\)

This means for 1 mole of reactant[MgCO\(_3\)], we will obtain 1 mole of product[MgO], i.e, the reactant and the product have a 1:1 mole ratio. When given the amount of reactant, we can find the theoretical yield by comparing the mole ratio. The ratio of actual yield given to this theoretical yield gives the percentage yield.

Percent Yield Formula

The percentage yield formula is calculated to be the experimental yield divided by theoretical yield multiplied by 100. If the actual and theoretical yield is the same, the percent yield is 100%. Usually, the percent yield is lower than 100% because the actual yield is often less than the theoretical value.

Percent Yield = (Actual Yield / Theoretical Yield) × 100 %

Percentage Yield Formula

Formula to Calculate Percent Yield

The formula to calculate the percent yield is:

Percentage Yield = (Actual Yield / Theoretical Yield) × 100 %

where,

Actual yield - it gives the amount of product obtained from a chemical reaction
Theoretical yield - it gives the amount of product obtained from the stoichiometric or balanced equation, using the limiting reactant to determine the product
Units for both actual and theoretical yield need to be the same (moles or grams)

Examples on Percent Yield

Example 1: During a chemical reaction, 0.5 g of product is made. The maximum calculated yield is 1.6 g. What is the percent yield of this reaction?

Solution:

We know that according to Percent Yield Formula,

Percentage yield = (Actual yield/Theoretical yield)× 100%

= 0.5/1.6× 100%

= 31.25%

Therefore, the percentage yield of this reaction is 31.25%.
Example 2: During a chemical reaction 1.8 g of product is made. The maximum calculated yield is 3.6 g. What is the percent yield of this reaction?

Solution:

We know that according to Percent Yield Formula,

Percentage yield = (Actual yield/Theoretical yield)× 100%

= 1.8/3.6× 100%

= 50%

Therefore, the percentage yield of this reaction is 50%.
Example 3: If the percentage yield is 45% with the theoretical yield as 4g, what would the actual yield be? Calculate using the percentage yield formula.

Solution:

Using the percentage yield formula,

Percentage yield = (Actual yield/Theoretical yield)× 100%

45 = Actual yield/4 × 100

Actual yield = 1.8

Therefore, the actual yield is 1.8g

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Practice Questions on Percent Yield

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FAQs on Percent Yield

What is Meant By Percent Yield?

Percent yield is a measure of the actual number of moles obtained for any reactant in any reaction in comparison to the predicted or theoretical yield.

What is Meant by Percent Yield Formula?

The percent yield formula is the percent ratio of actual yield to the theoretical yield. Yield is a measure of the quantity of moles of a product formed in relation to the reactant consumed, obtained in a chemical reaction, usually expressed as a percentage. The amount of product actually made compared with the maximum calculated yield is called the Percent yield. The formula is (Actual Yield / Theoretical Yield) × 100 %

What is the Formula to Calculate the Percent Yield?

The formula to calculate the percentage yield is:

Percent Yield = (Actual Yield / Theoretical Yield) × 100 %

where,

Actual yield - it gives the amount of product obtained from a chemical reaction
Theoretical yield - it gives the amount of product obtained from the stoichiometric or balanced equation, using the limiting reactant to determine the product
Units for both actual and theoretical yield need to be the same (moles or grams)

Why do Use the Percent Yield Formula?

The percent yield is also used in the field of chemistry, where the percentage yield of a chemical reaction is considered very important. The formula to calculate the percentage yield is to compare the yield or the quantity of the product that is obtained.

Why is the Percent Yield not 100% When the Formula is Used?

In most cases, the percent yield is less than 100% because the actual yield is often less than the theoretical value. This is due to the incomplete or competing reactions and loss of samples during recovery.