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Chapter 4
Stoichiometry
Gasoline and Other Fuels
Hydrocarbons – What were these again?
Alkanes: General Formula CnH2n+2
Isomers
Combustion Reaction:
Stoichiometry
Calculating amounts of reactants and products
from chemical equations.
The mass-mole-number relationships in a chemical reaction.
MASS(g)
of compound A
MASS(g)
of compound B
(g/mol) of
compound A
AMOUNT(mol)
of compound A
The Mole Hole
balanced equation
Avogadro’s number
(molecules/mol)
MOLECULES
(or formula units)
of compound A
(g/mol) of
compound B
AMOUNT(mol)
of compound B
Avogadro’s number
(molecules/mol)
MOLECULES
(or formula units)
of compound B
Example: Iron (III) oxide reacts with carbon monoxide
and produces iron metal and carbon dioxide.
(a) Write a balanced equation for this rxn.
(b) How many moles of iron are formed from 2.50
moles of iron(III) oxide?
(c) How many grams of CO2 are formed by 2.50 moles
of Fe2O3?
(d) How many grams of iron are produced from 1.00
kilogram of iron (III) oxide?
(e) How many grams of CO are required to react with
75.0 grams of iron (III) oxide?
(f) What mass of CO2 will be produced if 50.0 grams of
iron are formed?
Writing an Overall Equation for a Reaction Sequence
PROBLEM:
Roasting is the first step in extracting copper from chalcocite,
Cu2S. In the next step, copper(I) oxide reacts with powdered
carbon to yield copper metal and carbon monoxide gas. Write a
balanced overall equation for the two-step process.
PLAN:
SOLUTION:
write balanced equations for each step
2Cu2S(s) + 3O2(g)
cancel reactants and products common
to both sides of the equations
2Cu2O(s) + 2C(s)
sum the equations
2Cu2S(s)+3O2(g)+2C(s)
2Cu2O(s) + 2SO2(g)
4Cu(s) + 2CO(g)
4Cu(s)+2SO2(g)+2CO(g)
Exercise 6
Work problems 1-3 in groups and place your
answers on the board.
Chemical Reactions that Involve Limiting
Reactants
A BLT sandwich requires 2 slices of bread, 1 leaf
of lettuce, 4 slices of bacon, and 3 tomato
slices.
How many sandwiches could you make if you
were given:
4 slices of bread
5 leaves of lettuce
12 slices of bacon
10 tomatoes
Nuclear engineers use chlorine trifluoride in the processing
of uranium fuel for power plants. This extremely reactive
substance is formed as a gas in special metal containers by
the reaction of elemental chlorine and fluorine.
(a) Suppose the box shown at left represents a
container of the reactant mixture before the
reaction occurs (with chlorine colored green).
Name the limiting reactant, and draw the
container contents after the reaction is
complete.
Cl2(g) + 3 F2(g)  2 ClF3(g)
(b) When the reaction is run again with 0.750 mol of
Cl2 and 3.00 mol of F2, what mass of chlorine trifluoride
will be prepared?
Example: If 5.000 grams of aluminum and 5.000 grams
of hydrochloric acid are placed in a rxn vessel a rxn.
occurs in which aluminum chloride and hydrogen
gas are produced.
(a) How many grams of hydrogen gas will be produced?
(b) How many grams of aluminum chloride are
produced?
(c) Which is the limiting reactant?
(c) What mass of the limiting reactant remains?
(d) Students perform this rxn in lab and obtain 0.1256
grams of hydrogen gas. What is their percent
yield?
Exercise 6 (cont.)
Do problems 4,5,6,7,8,9,10 and 14.
Calculating Amounts of Reactants and Products
for a Reaction in Solution
A student placed 15.0 mL of 0.200 M lead (II) nitrate
into a flask. He adds 30.0 mL of 0.200 M potassium
Iodide solution. What mass of precipitate forms?
Careful, you have both quantities of the reactants.
What does this mean to you?
• Do Exercise 6, # 12.
• Do Exercise 6, #’s 11 and 13. Note: These are
cumulative skill problems.
Another Problem: Mercury and its compounds
have many uses, from fillings for teeth (as an alloy
with silver, copper, and tin) to the industrial
production of chlorine. Because of their toxicity
soluble mercury compounds, such mercury(II)
nitrate, must be removed from industrial
wastewater. One removal method reacts the
wastewater with sodium sulfide solution to produce
solid mercury(II) sulfide and sodium nitrate solution.
In a laboratory simulation, 0.050L of 0.010M
mercury(II) nitrate reacts with 0.020L of 0.10M
sodium sulfide. How many grams of mercury(II)
sulfide form?