General Chemistry

1. STOICHIOMETRY
Chapter 9
Modern Chemistry
S.Martinez – Spring 2011

2.  Ch 9 Vocab – 8 words
 Lab # 6 & Lab # 7 Reports are due

3. Intro to Stoichiometry
 Composition vs Reaction Stoichiometry
 Comp – mass relationship of elements in
compounds
 Reaction – mass relationship between reactants
and products in chem rxn

4. 4 Types of Reaction-Stoichiometry
Problems
 Type 1:
 Given and unknown amounts are in moles
 Type 2:
 Given amt in moles and unknown needs to be in
grams
 Type 3:
 Given amt in grams and unknown needs to be in
moles
 Type 4:
 Given and unknown amts are in grams

5. Mole Ratio
 Any of the reaction problems can be solved
using ratios.
 Mole ratio is derived from the coefficients in a
balanced chemical equation.
 Ex: Decomposition of aluminum oxide by
electrolysis
 2Al2O3  4Al + 3O2

6.  Ex: Decomposition of aluminum oxide by
electrolysis
 Determine the amount of Aluminum that can be
produced from 13.0 mol of aluminum oxide.
Equation
s
2Al2O3  4Al + 3O2
Moles 2 moles 4 moles 3 moles
Molar
mass
Grams

7. Molar Mass as a Ratio
 Using the same problem, calculate the number
of grams of aluminum equivalent to 26.0
moles of aluminum.

8. Section 9.2
 Chemical Equations help make predictions
about chemical reactions without having to run
the reactions in the laboratory.
 All of the reaction stoichiometric problems are
theoretical, meaning we are assuming ideal
conditions in which all reactants are converted
into products.
 Theoretical stoichiometric calculations show
the maximum amt of product that could be
obtained.

9. Problem Type #1
+Amt of given
substance in
mol
Amt of
unknown
substance in
mol

10.  In a spacecraft, the carbon dioxide exhaled by
astronauts can be removed by its reaction with
lithium hydroxide, LiOH.
How many moles of lithium hydroxide are
required to react with 20 mol of carbon
dioxide, the average amount exhaled by a
person each day?
CO2 +2LiOH  Li2CO3 + H2O

11.  Answer: 40 moles of LiOH

12.  Ammonia is widely used as a fertilizer and in
many household cleaners. How many moles
of ammonia, NH3, are produced when 6 mol of
hydrogen gas react with an excess of nitrogen
gas?

13.  Answer: 4 moles of Ammonia

14.  The decomposition of potassium chlorate is
used as a source of oxygen in the laboratory.
How many moles of potassium chlorate are
needed to produce 15 mol of oxygen?

15.  Answer: 10 mol KClO3

16.  The elements Lithium and oxygen react
explosively to form lithium oxide. How many
moles of lithium oxide will form if 2 mol of
lithium react? (synthesis rxn)

17.  Answer: 1 mole of Lithium Oxide

18.  The disinfectenct hydrogen peroxide, H2O2,
decomposes to form water and oxygen gas.
How many moles of oxygen will result from the
decomposition of 5 mol of hydrogen peroxide?

19.  Answer: 2.5 mol of oxygen

20. Problem Type 2
 Starting in moles ending in grams
 Moles to moles to grams

21.  In photosynthesis, plants use energy from the
sun to produce glucose, C6H12O6, and oxygen
from the reaction of carbon dioxide and water.
What mass, in grams, of glucose is produced
when 3.00 mol of water react with carbon
dioxide?

23.  In photosynthesis, plants use energy from the
sun to produce glucose, C6H12O6, and oxygen
from the reaction of carbon dioxide and water.
What mass, in grams, of glucose is produced
when 3.00 mol of water react with carbon
dioxide?
 CO2 + H2O  C6H12O6 + O2

24.  In photosynthesis, plants use energy from the
sun to produce glucose, C6H12O6, and oxygen
from the reaction of carbon dioxide and water.
What mass, in grams, of glucose is produced
when 3.00 mol of water react with carbon
dioxide?
 CO2 + H2O  C6H12O6 + O2
 6CO2 + 6H2O  1C6H12O6 + 6O2

25.  In photosynthesis, plants use energy from the
sun to produce glucose, C6H12O6, and oxygen
from the reaction of carbon dioxide and water.
What mass, in grams, of glucose is produced
when 3.00 mol of water react with carbon
dioxide?
 CO2 + H2O  C6H12O6 + O2
 6CO2 + 6H2O  C6H12O6 + 6O2

3 mol ? grams

26.  6CO2 + 6H2O  C6H12O6 + 6O2
 3.00 mol of H20 x (1 mol glucose/6 mol of water) =
0.500 mol of glucose
 0.500 mol of glucose x (180.18 grams/mol)
 = 90.09 grams of glucose
 C – (6 x 12.01) = 72.06
 H– (12 x 1.01) = 12.12
 O – ( 6 x 16.00) = 96.00
 Total molarmass = 180.18 g/mol

27.  What mass of carbon dioxide, in grams, is
needed to react with 3.00 mol of water in the
above photosynthetic reaction?
 6CO2 + 6H2O  C6H12O6 + 6O2

28. 6CO2 + 6H2O  C6H12O6 + 6O2

29.  6CO2 + 6H2O  C6H12O6 + 6O2
 3.00 mol of water x ( 6 mol of water/6 mol of
CO2 ) = 3.00 mol of CO2
 3.00 mol of CO2 x (44.01 grams/mole) = 132.
grams of carbon dioxide
 C – (1 x 12.01) = 12.01
 O – (2 x 16.00) = 32.00
 Molar mass = 44.01 grams/mole

30.  When magnesium burns in the air, it combines
with oxygen to form magnesium oxide. What
mass, in grams, of magnesium oxide is
produced from 2.00 mol of magnesium?

31.  When magnesium burns in the air, it combines
with oxygen to form magnesium oxide. What
mass, in grams, of magnesium oxide is
produced from 2.00 mol of magnesium?
 2Mg + O2  2MgO

32. 2Mg + O2  2MgO

33.  When magnesium burns in the air, it combines
with oxygen to form magnesium oxide. What
mass, in grams, of magnesium oxide is
produced from 2.00 mol of magnesium?
 2Mg + O2  2MgO

34.  2Mg + O2  2MgO
 2.00 mol Mg x (2 mol of MgO/2 mol of Mg) =
2.00 mol MgO
 2.00 mol MgO x (40.31 grams/mole) = 80.6
grams

35.  What mass in grams of oxygen combines with
2.00 mol of magnesium in this same reaction?
 2Mg + O2  2MgO

36.  What mass of glucose, C6H12O6 (molar mass
180.18 g/mol, solved from a previous
problem) can be produced from a
photosynthesis reaction that occurs using 10
mol CO2?
 6CO2 + 6H2O  C6H12O6 + 6O2

37.  Answer: 300 grams of glucose

38.  When sodium azide is activated in an
automobile airbag, nitrogen gas and sodium
are produced according to the equation:
NaN3  Na + N2
If 0.500 mol of NaN3 react, what mass in grams
of Nitrogen would result?

39.  Answer: 21.0 grams of Nitrogen

40.  Carborundum, SiC, is a hard substance made
by combining silicon dioxide with coke(C) as
follows:
SiO2 + 3C  SiC + 2CO
What mass in grams of SiC is formed from the
complete reaction of 2.00 mol of carbon?

41.  Answer: 26.7 grams of SiC

42.  Coal can be converted to methane gas by a
process called coal gasification. The equation
for the reaction is the following:
2C + 2H2O  CH4 + CO2
What mass in grams of carbon is required to
react with water to form 1.00 mol of CH4?

43.  Answer: 24.0 grams C

44. Problem Type 3
 Starting in grams ending in moles
 Grams to moles to moles

45.  The 1st
step in the industrial manufacture of
nitric acid is the catalytic oxidation of
ammonia.
 NH3 + O2  NO + H2O
 The reaction is run using 824 g of ammonia
and excess oxygen.
 How many moles of nitrogen monoxide are
formed?
 How many moles of water are formed?

46.  4NH3 + 5O2  4NO + 6H2O
 The reaction is run using 824 g of ammonia
and excess oxygen.
 How many moles of nitrogen monoxide are
formed?
 How many moles of water are formed?

47.  48.3 mol NO
 72.5 mol of water

49. Problem Type 4
 Starting in grams ending in grams
 Grams of given to moles of given to moles of
unknown to grams of unknown

50.  Tin (II) fluoride, SnF2, is used in some
toothpastes. It is made by the reaction of tin
with hydrogen fluoride according to the
following equation.
 Sn + 2HF  SnF2 + H2
 How many grams of SnF2 are produced from
the rxn of 30.00 g of HF with Sn?

51. Sn + 2HF  SnF2 + H2
Sn 2HF SnF2 H2
Moles
Given
Molar mass
Moles calc.
Mass calc.

52.  117.5 g SnF2

53.  Laughing gas (dinitrogen monoxide) is
sometimes used as an anesthetic in dentistry.
It is produced when ammonium nitrate is
decomposed according to the following rxn.
 NH4NO3  N2O + H2O
 If 360 g of ammonium nitrate are decomposed
how many grams of dinitrogen monoxide will
be formed?