Limiting Reagents

Overview: This tutorial discusses limiting reagents, demonstrates how theoretical and percent yields are determined, and presents possible factors that may preclude the achievement of the full theoretical yield in practice.

Skills:

New terms:


Typically in chemical reactions between two reagents, both are not used completely. In general, one may be used completely while some amount of the other reagent(s) may remain after the reaction has occurred. Those that remain are said to react in excess. The reactant that is used completely is the limiting reagent. The limiting reagent determines the amount of product(s) at the end of the reaction as well as how much remains of the reactant(s) that occurred in excess. When the limiting reagent is completely used the reaction stops. Why would chemists be interested in this information? Answer

In order to determine which reactant is the limiting reagent, take each reactant separately and assume that it is the limiting reagent. The reactant that produces the least amount of product must be the limiting reagent.

Example.

Tin (Sn) and iodine (I2) react to produce tin iodide (SnI4). If there are 10.00 g of tin and 40.00 g of I2 at the beginning of the reaction, what is the maximum amount of SnI4 that may be produced?

What is happening in this reaction? We have iodine, which is a black crystalline solid reacting with tin (a grey-white solid metal solid) to form SnI4. So the skeleton equation is Sn + I2 SnI4.

Reasons for not achieving the theoretical yield

What are some possible reasons why the theoretical yield is not achieved? Answer


Advanced Applications: An organic chemist at Washington University develops methods for synthesizing pharmacologically active compounds.

Summary

After completing this review, you should be able to determine the limiting reagent and be able to calculate the amount of product formed from the limiting reagent. You should also understand the percent yield of the reaction.


Practice Quizzes: Stoichiometry/Limiting Reagents/Solutions

These two quizzes cover the three tutorial modules Stoichiometry, Limiting Reagents, and Solutions. You will probably want to review all three of these modules before trying the quiz.

Note: You will need a pencil, scratch paper, calculator, periodic table and equation sheet to work the practice quiz. Quiz questions are timed (4 minutes per question).

Open Periodic Table in a separate browser window.

Open Equations/Constants Page in a separate browser window.






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