Percent yield is used to measure the efficiency of a chemical reaction or a process. It compares the actual yield of a reaction to the theoretical yield, 

Actual Yield = 

Theoretical Yield = the maximum amount of product that should be obtained based on stoichiometric calculations. 

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

A percent yield of 100% indicates that the actual yield matches the theoretical yield perfectly, suggesting a highly efficient reaction. A percent yield lower than 100% indicates that the actual yield is lower than expected, indicating inefficiencies such as incomplete reactions, side reactions, or losses during purification or separation processes.

Percent error is a measure of how close the experimental value is to the true or expected value.

The formula is as follows:

Percent Error = [(|Experimental Value - Accepted Value|) / Accepted Value] x 100%

A percent error of 0% indicates that the experimental value is an exact match to the accepted value. A positive percent error indicates that the experimental value is higher than the accepted value, while a negative percent error indicates that the experimental value is lower. The magnitude of the percent error indicates the degree of deviation from the accepted value.