Enter the total reagent and limiting reagent into the calculator to determine the excess reagent. This calculator can also evaluate any of the variables given the others are known.

Excess Reagent Formula

The following formula is used to calculate the excess reagent in a chemical reaction. Variables:

ER = (TR - LR) 

  • ER is the excess reagent TR is the total reagent LR is the limiting reagent

To calculate the excess reagent, subtract the limiting reagent from the total reagent. The result is the amount of excess reagent.

What is an Excess Reagent?

An excess reagent, in chemistry, refers to the reactant that is in surplus quantity during a chemical reaction. It is the substance that completely reacts with the limiting reagent (the reactant that is completely consumed in the reaction) and still remains unreacted because there is more of it than necessary for the reaction to go to completion. The excess reagent is left over after the limiting reagent is completely used up in the reaction.

How to Calculate Excess Reagent?

The following steps outline how to calculate the Excess Reagent using the formula: ER = (TR – LR).

  1. First, determine the value of the Total Reagent (TR).
  2. Next, determine the value of the Limiting Reagent (LR).
  3. Subtract the value of the Limiting Reagent (LR) from the value of the Total Reagent (TR) using the formula ER = (TR – LR).
  4. Finally, calculate the Excess Reagent (ER).
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem:

Use the following variables as an example problem to test your knowledge.

Total reagent (TR) = 50

Limiting reagent (LR) = 30