# 11-3: Limiting Reactants and Percent Yield

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11-3: Limiting Reactants and Percent Yield

Limiting Reactant Pretend that you want to put together some toy cars from some pre-assembled bodies. All you had to do is add the wheels. If you have 22 wheels and 6 bodies, how many cars can you make? Well, 6 cars x 4 wheels = 24 total wheels needed. Since you don’t have that many wheels, the wheels that you DO have limit how many cars that you can make.

Limiting Reactant The same is true in chemistry.
Consider the following chemical equation… 2H2 + O2  2 H2O Well, there has to be SOME perfect ratio of hydrogen gas to oxygen gas. If that perfect ratio isn’t what you have in reality, one of the two reactants LIMITS how much product that you can make.

Limiting Reactant Limiting reactant (reagent): the reactant that limits the amount of product formed in a chemical reaction You CANNOT identify the limiting reactant just by looking at whichever reactant that you have the least. You have to use stoichiometry to find the limiting reactant.

Steps in finding the LR Write and balance your chemical equation.
Calculate the mass of a product formed by each reactant. The reactant that produces the smaller amount of product is your limiting reactant.

Sample Problem #5 (pg. 368)

Sample Problem #6 (pg. 370)

Percent Yield Percent yield: a comparison between what you actually produce in an experimental trial and what you should theoretically produce. Theoretical yield: amount of product that should be produced, based on calculations Actual yield: amount of product that is actually produced in your experiment.

Percent Yield Percent yield = (actual yield)/(theoretical yield) x 100
Sample problem #7 (pg. 372) Practice problem #14 (pg. 372)