How do the theoretical yield, actual yield, and percent yield change (or not change) if 20 g of substance A is reacted with 20 g of substance B
The Correct Answer and Explanation is:
In a chemical reaction, theoretical yield, actual yield, and percent yield are key concepts to understand in assessing the efficiency of the reaction. Here’s how they relate to the amounts of substance A and substance B:
Theoretical Yield:
The theoretical yield refers to the maximum amount of product that can be formed from the given amounts of reactants, based on stoichiometric calculations. It assumes that the reaction goes to completion without any loss of product.
To calculate the theoretical yield, we need to:
- Determine the limiting reagent, which is the reactant that will run out first and thus limit the amount of product that can be formed.
- Use stoichiometry (moles, molar ratios) to find the maximum amount of product that can be formed from the limiting reagent.
If 20 g of substance A is reacted with 20 g of substance B, the limiting reagent must be identified by converting the masses of both substances into moles and comparing their molar ratios as given in the balanced equation. The reactant with the lesser amount of moles relative to the required stoichiometric ratio will be the limiting reagent, and its amount will determine the theoretical yield.
Actual Yield:
The actual yield is the amount of product actually obtained when the reaction is carried out in the laboratory. This value is determined by performing the reaction and measuring the product obtained. The actual yield can be less than the theoretical yield due to factors like incomplete reactions, side reactions, or loss of product during handling.
Percent Yield:
The percent yield compares the actual yield to the theoretical yield and expresses it as a percentage. It is calculated using the formula:
[
\text{Percent Yield} = \left(\frac{\text{Actual Yield}}{\text{Theoretical Yield}}\right) \times 100
]
If 20 g of substance A and 20 g of substance B are used, the percent yield depends on the actual yield measured in the experiment. If all conditions are ideal and the reaction proceeds to completion, the percent yield will be 100%. However, in practical scenarios, the percent yield is usually less than 100% due to factors like incomplete reactions, side products, or losses during the process.
Summary:
- The theoretical yield is calculated based on the limiting reagent and stoichiometric ratios.
- The actual yield is the amount of product obtained experimentally.
- The percent yield is the ratio of the actual yield to the theoretical yield, multiplied by 100.
In this scenario, the theoretical yield depends on which substance (A or B) is the limiting reagent, and the actual yield will likely be less than the theoretical yield, leading to a percent yield that is less than 100%.