LIMITING REAGENT
is the reactant that is completely consumed in a reaction, thereby limiting the amounts of products formed.

To determine the limiting reagent, calculate the amount of product (moles or grams) that can be formed
from EACH reactant.  The reactant producing the smallest amount of product is the limiting reagent.

EXAMPLE 1
A mixture of 4.0 moles of A and 3.0 moles of B is allowed to react and produce C according to the
following equation.

    2 A + B ----> 2 C

A.    What is the limiting reagent?              [The limiting reagent is A.]
B.    How much C could be formed?        [4 mol C]
 

EXAMPLE 2
A mixture of 35.0 g of hydrogen and 270. g of oxygen is allowed to react and produce water.

A.    What is the limiting reagent?        [The limiting reagent is O₂.]
B.    What mass of water could be formed?    [304 g H₂O]

The theoretical yield is the amount calculated from the limiting reagent.

ACTUAL YIELD is the MEASURED amount of product that is obtained after the reaction has taken place.

Percent Yield =      actual yield  x 100
                          theoretical yield

EXAMPLE 3
Carbon tetrachloride (CCl₄) was prepared by reacting 100. g of carbon disulfide (CS₂) and 100. g of chlorine
according to the following equation.

    CS₂ + 3 Cl₂ ---> CCl₄ + S₂Cl₂

Calculate the percent yield if 65.0 g of CCl₄ was obtained from the reaction.
[89.9%]