1. Reaction Stoichiometry

2. I. Introduction to Reaction Stoichiometry
A. Definitions
1. Stoichiometry - deals with the amount
of reactants and products in chemical
reactions
2. Mole Ratio - conversion factor that
relates the number of moles of any two
substances involved in a chemical
reaction

3. B. Types of Stoichiometry Problems
(A is the given, B is the unknown)
1. mole-mole (mole A  mole B)
2. mole-mass (mole A  mass B)
3. mass-mole (mass A  mole B)
4. mass-mass (mass A  mass B)

4. *All problems will include a mole B conversion factor mole A
C. Diagram
A is the given
B is what you need to find - the unknown
*All problems will include a mole B
conversion factor mole A
1 mole A # mole B molar mass B
MASS A > MOLE A > MOLE B > MASS B
molar mass A # mole A mole B

5. A. 2H2 + O2 ----------> 2H2O
III. Mole Ratios and Coefficients in Equations
A. 2H2 + O > 2H2O
H2, O ) H2, H2O ) O2, H2O
2 mol H mol O mol H mol H2O mol O mol H2O
1 mol O mol H mol H2O 2 mol H mol H2O 1 mol O2
B. 2KClO > 2KCl + 3O2
1) KClO3, KCl )KClO3 , O ) KCl, O2

6. A – Given B - find of Cl2? 4.0 mol Na X 1.0 mol Cl2 = 2 mol Cl2
II. Solving Stoichiometry Problems
(All Problems Include Mole Ratios)
Mole-Mole
electricity
1. 2 Na + Cl > 2NaCl
A – Given B - find
a) 4 moles of Na will react with (?) moles
of Cl2?
4.0 mol Na X mol Cl2 = 2 mol Cl2
mol Na

7. A. Mole –Mole Problem 2 Na + Cl2 ----------> 2NaCl
A - Given B - Find
b)6 moles of Na will form (?) moles of NaCl?
6 mol Na X 2 mol NaCl = 6 mol NaCl
mol Na

8. 1. CaO + H2O ----------> Ca(OH)2
B. Mole-Mass
1. CaO + H2O > Ca(OH)2
A B
a)2 moles of CaO will produce(?)grams of Ca(OH)2
2 mol CaO x 1 mol Ca(OH)2 x 74.1g Ca(OH)2 =
mol CaO mol Ca(OH)2
148 g Ca(OH)2

9. CaO + H2O ----------> Ca(OH)2
b) How many grams of CaO are needed to
form 2 moles of Ca(OH)2?
2 mol Ca(OH)2 x 1 mol CaO x g CaO =
mol Ca(OH) mol CaO
112g CaO

10. Mass-Mole
1. Zn + 2HCl > ZnCl2 + 2H2
How many moles of zinc chloride are
formed when grams of zinc react with hydrochloric acid?
196.2g Zn x 1 mol ZnCl2 = mol ZnCl2
g Zn

11. 1. Zn + 2HCl ----------> ZnCl2 + 2H2
b) How many moles of zinc are necessary to
form grams of zinc chloride?
67.70g ZnCl x 1 mol ZnCl2 x 1 mol Zn =
g ZnCl2 1 mol ZnCl2
.4967 mol Zn

12. 1. CH4 + 2O2 ----------> CO2 + 2H2O
D. Mass-Mass
1. CH O > CO H2O
How many grams of carbon dioxide are formed when 64.0 grams of oxygen react with methane?
64.0g O2 x 1 mol O2 x 1 mol CO2 x 44.0g CO2 =
g O mol O mol CO2
44.0g CO2

13. 1. CH4 + 2O2 ----------> CO2 + 2H2O
b) How many grams of methane are needed to
produce 48.0 grams of water?
48.0g H2O x 1 mol H2O x 1 mol CH4 x 16.0g CH4 =
g H2O 2 mol H2O 1 mol CH4
21.3g CH4

14. reaction and determine the amount of
III. Limiting Reactant
A. Definitions
1. limiting reactant – limits the extent of
reaction and determine the amount of
product (reactant that is used up first)
2. excess reactant – portion of reactant
that remains after a reaction is
complete

15. B. What are some examples that model
limiting reactant and excess reactant?
1. hamburger + bun
2. cake recipe requires 2 eggs and
3 cups of flour, and 1 cup sugar

16. C. How is the Limiting Reactant
Determined?
1. Divide number of moles of each
reactant by its coefficient in the
balanced equation
2. The substance with the smaller
number is the limiting reactant.
3. The substance with the larger number
is the excess reactant.

17. Example Determine the limiting reactant,
the excess reactant reactant and the number of
moles of each product? (6 moles of H2 combined
with 3 moles of N2)
H2(g) N2(g)  2NH3(g)
6 mol mol
6/3 = /1 = 1
H2 is excess N2 is limiting
b) 3 mol N2 x 2 mol NH3 = 6 mol NH3
mol N2

18. Determine the limiting reactant, the excess
reactant and the number of moles of each product
2. Zn(s) + 2HCl(aq)  ZnCl2(aq) + H2(g)
2.5 mol Zn +3.5 mol HCl are combined
2.5/1 = /2 = 1.75
Zn is excess HCl is limiting
b) 3.5 mol HCl x 1 mol ZnCl2 = mol ZnCl2
mol HCl
c) 3.5 mol HCl x 1 mol H2 = mol H2
mol HCl

19. IV. Percent Yield
Definitions
1. theoretical yield – maximum amount of
product that can be produced from a given
amount of reactant
2. actual yield – amount of product actually
produced during a reaction carried out in
the lab
3. percent yield – ratio of actual yield to the
theoretical yield expressed as a percent

20. 1. Determine theoretical yield ( mass-
% Yield = Actual yield (experiment results) X 100%
Theoretical yield (stoichiometric calculations)
B. Procedure
1. Determine theoretical yield ( mass-
mass stoichiometric calculation)
2. Divide actual yield (experiment results
in grams) by theoretical yield
3. Multiply by 100% to get percent yield

21. 1. Zinc reacts with iodine in a synthesis reaction.
a. Determine the theoretical yield if 125.0g of zinc is used.
b. Determine the % yield if the mass of the product zinc
iodide recovered is 556g. Zn(s) + I2(s)  ZnI2(s)
a)125.0g Zn x 1 mol Zn x 1 mol ZnI2 x 329.2g ZnI2 = 707.4g
g Zn 1 mol Zn mol Zn
Theoretical Yield is g ZnI2
b) Actual yield………… = % (percent yield)
Theoretical yield……

22. 2. Water decomposes when subject to an electric current
to form hydrogen gas and oxygen gas. In the lab, 60.0 g of
oxygen is recovered when 72.0g of water is decomposed.
What is the theoretical yield? What is the percent yield?
electricity
2 H2O  2H O2
72.0g H2O x 1 mol H2O x 1 mol O2 x 32.0g O2 = 64.0g O2
g H2O 2 mol H2O mol O2
Actual Yield…………60.0g = % (percent yield)
Theoretical Yield… g