Problem 72 - Chemistry: The Central Science

Question

(a) Define the terms theoretical yield, actual yield, and percent yield. (b) Why is the actual yield in a reaction almost always less than the theoretical yield? (c) Can a reaction ever have \(110 \%\) actual yield?

Step-by-Step Solution

Answer

The theoretical yield is the maximum amount of product that can be formed in a chemical reaction, based on stoichiometry and the limiting reagent. Actual yield is the measured amount of product obtained from a reaction, usually less than the theoretical yield due to factors like incomplete reactions, side reactions, and losses during the process. Percent yield is the ratio of the actual yield to the theoretical yield, multiplied by 100. Actual yield is generally less than theoretical yield due to factors like incomplete reactions, side reactions, losses during the process, and impurities in reactants. A reaction cannot have a 110% actual yield, as the theoretical yield is the maximum product amount possible. Percent yield greater than 100% indicates an error in calculations or measurements.

Step 1: Definition of Theoretical Yield

The theoretical yield is the maximum amount of product that can be formed during a chemical reaction, based on the stoichiometry of the balanced chemical equation. It is calculated using the limiting reagent present in the reaction and the balanced equation.

Step 2: Definition of Actual Yield

The actual yield is the amount of product that is actually obtained from a chemical reaction, which can be measured experimentally. It is usually less than the theoretical yield due to various factors including losses during the reaction process, side reactions, and incomplete reactions.

Step 3: Definition of Percent Yield

Percent yield is the ratio of the actual yield to the theoretical yield, multiplied by 100. It is a measure of the efficiency of a chemical reaction in producing the desired product. The formula for percent yield is: \( Percent \: Yield = \frac{Actual \: Yield}{Theoretical \: Yield} \times 100 \%)

Step 4: Reasons for Actual Yield Being Less Than Theoretical Yield

The actual yield is generally less than the theoretical yield due to various factors. Some of the possible factors include: 1. Incomplete reactions: The reactants may not completely convert into products, leaving unreacted starting materials. 2. Side reactions: Some of the reactants may undergo other chemical reactions, reducing the quantity of reactants available for the main reaction. 3. Losses during the process: Some of the product may be lost during filtration, evaporation, or other processing steps. 4. Impurities in reactants: The presence of impurities in the reactants can interfere with the reaction, reducing the amount of product formed.

Step 5: Possibility of 110% Actual Yield

A reaction can never have an actual yield of 110%. The actual yield cannot be greater than the theoretical yield, as the theoretical yield represents the maximum amount of product that can be formed based on the stoichiometry of the reaction. A percent yield greater than 100% indicates an error in calculations or measurements.