1.1 What is Chemistry?

12.3. Limiting Reactant and Percent Yield http://www.ck12.org

If the yield is 87.5%, we can perform the following calculation:

Percent Yield=

Actual Yield

Theoretical Yield

×100%

Actual Yield= (Theoretical Yield)(

Percent Yield

100%

)

Actual Yield= ( 8 .62 g)(

87 .5%

100%

)

Actual Yield= 7 .54 g

7.54 grams of ammonia were actually produced in this reaction.

Lesson Summary

• Chemical reactions can be studied in terms of the amounts of reactants that are present and the amount of
  products that are formed.


• The balanced chemical equation describes the relative amounts of reactants and products that are consumed
  and generated by a given chemical process.


• Reactants combine in fixed mole ratios.


• The amount of each reactant needed to generate a certain amount of product can be determined with stoichio-
  metric calculations.


• In cases where one reactant is used up before the others, we can describe the reaction in terms of a limiting
  reactant and one or more excess reactants.


• The actual and theoretical yields for a given reaction are often related by calculating a percent yield.


• The reaction table method provides a way to organize the information needed to perform stoichiometry
  calculations and to answer quantitative questions about various chemical reactions.

Lesson Review Questions

1. Urea (NH 2 ) 2 CO is prepared by reacting ammonia with carbon dioxide according to the following equation:
   2NH 3 (g) + CO 2 (g)→(NH 2 ) 2 CO(aq) + H 2 O(l). In one experiment, 637.2 g of NH 3 is allowed to react with
   1142 g of CO 2.
   (a) Which of the two reactants is the limiting reagent?
   (b) Calculate the mass of(NH 2 ) 2 CO that could theoretically be formed by this reaction.


2. Hydrogen gas reacts explosively in the presence of oxygen to produce water.
   (a) Write the balanced chemical equation for this process.
   (b) If 1 mol of hydrogen gas and 1 mol of oxygen gas are placed in a container and ignited, how many moles
   of water will be produced?
   (c) Which will be the limiting reactant?
   (d) Which will be the excess reactant, and how much of the excess reactant will be left over?


3. If 1.00 grams of hydrogen gas and 1.00 grams of oxygen gas are placed in a container and ignited:
   (a) Which will be the limiting reactant?
   (b) Which will be the excess reactant?
   (c) What is the theoretical yield for water?