GEN CHEM | Limiting & Excess Reagents and Percent Yield

Limiting Reagent

it is fully used up in a reaction and determines the amount of product

Excess Reagent

it is present in quantities greater than necessary to ensure the other reactant is fully used up

How to find which are the limiting and excess reagent

1. Ensure that reaction is balanced.

2. For each reactant, calculate the amount of product formed in grams or moles.

3. Whichever gives the smallest grams or moles formed is the limiting reactant. The one that gives larger product formed is the excess reactant.

4. The smaller product formed is also the theoretical yield or product formed.

How to find mass of excess reagent after reaction

Use the mass of the limiting reagent to solve for the mass of the excess reagent consumed in the reaction. Subtract the consumed mass from the given mass to get the mass of the excess reagent.

Theoretical Yield

The predicted mass of a product after a reaction solved using the mass of the limiting reagent.

Actual Yield

The actual mass of product observed after are a reaction; may be less than the theoretical yield

Percent Yield

the percentage of the product that is observed a reaction compared to its theoretical yield

Percent Yield Equation

[Actual Yield]/[Theoretical Yield] x 100