20. __ Which variable is NOT needed to calculate percent vield? a. Theoretical yield b. Actual yield c. Reaction time d. Balanced equation

## Step 1<br />The percent yield is a measure of the efficiency of a chemical reaction. It is calculated by comparing the actual yield (the amount of product that is physically produced) to the theoretical yield (the maximum amount of product that could be produced based on stoichiometric calculations).<br /><br />## Step 2<br />The formula for calculating percent yield is:<br />### \( \text{Percent Yield} = \left( \frac{\text{Actual Yield}}{\text{Theoretical Yield}} \right) \times 100\% \)<br /><br />## Step 3<br />From the formula, it is clear that the reaction time is not needed to calculate the percent yield. The reaction time is not a factor in the formula for percent yield.