CHAPTER 4
Chemical Equations and
Stoichiometry
Test 1 return
Know elements 1-86 (symbol and spelling)
Formulas must be balanced
neutral (i.e. charge of 0)
Given table 3.1 (pg 107)
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Chem 105 Chpt 4 Lsn 8
Balanced equations
(from neutral formulas)
Conservation of matter (Lavoisier)
 Stoichiometry (stoichiometric coefficients)

 Relationship

between quantities prod. & react
5 step process (pg 146)
 Always
start with neutral formulas
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Chem 105 Chpt 4 Lsn 8
Conservation of
matter (Lavoisier)
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Chem 105 Chpt 4 Lsn 8
p.169b
Balancing equations
Aluminum and bromine combine to
produce aluminum bromide. This is
reacted with sulfuric acid (H2SO4).
Hydrogen bromide (HBr) and aluminum
sulfate are produced.
1.) Write the formulas for the reactants and
products.
2.) Balance the entire reaction.
3.) Verify an equal number of atoms on
reactant and product side.

Chem 105 Chpt 4 Lsn 8
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Chem 105 Chpt 4 Lsn 8
Balancing an ionic equation
Number of atoms and charge must be
balanced.
 Aluminum oxide (Al2O3) and monatomic
hydrogen gas combine to form water and
aluminum ion.
 Write formulas for balanced reactants and
products.
 Balance the reaction.
 Double check.
 Al2O3 + 6 H+  2 Al3+ + 3 H2O

Chem 105 Chpt 4 Lsn 8
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Balancing with a polyatomic ion
Remember to keep the ion together
 Phosphoric acid (H3PO4) and barium
hydroxide combine to form barium
phosphate and water.
 Balance the starting material formulas and
then the equation
 H3PO4 + Ba(OH)2  Ba3(PO4)2 + H2O
 2H3PO4 +3 Ba(OH)2  Ba3(PO4)2 +6 H2O

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Chem 105 Chpt 4 Lsn 8
Mass relationships
(use stoichiometric relation)
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Chem 105 Chpt 4 Lsn 8
Mass relationships
Na2SO4 (aq)+ BaCl2 (aq)  NaCl (aq) + BaSO4 (s)
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Chem 105 Chpt 4 Lsn 8
Fig. 4.8, p.159
Mass relationships
Na2SO4 (aq)+ BaCl2 (aq)  NaCl (aq) + BaSO4(s)
Balance the equation
 How many moles of NaCl will be produced from
0.81 moles of Na2SO4?
 How many grams of NaCl will be produced from
0.81 moles of Na2SO4?
 How many grams of BaSO4 will be produced from
3.76 grams of BaCl2?

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Chem 105 Chpt 4 Lsn 8
p.149
Limiting reactant (reagent)
Which reactant is limiting?
 How much of product can be formed?
 Ammonia gas can be prepared by the
reaction of a metal oxide such as calcium
oxide with ammonium chloride. If 112g of
CaO and 224g of NH4Cl are mixed, what
mass of NH3 can be produced?

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Chem 105 Chpt 4 Lsn 8
Limiting reactant (reagent)
24. Aluminum chloride, AlCl3, is made by
treating scrap aluminum with chlorine.
2 Al (s) + 3 Cl2 (g)  2 AlCl3 (s)

If you begin with 2.70 g of Al & 4.05 g of Cl2
a) Which reactant is limiting?
b) What mass of AlCl3 can be produced?
c) What mass of the excess reactant
remains after the hexane has been
burned?
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Chem 105 Chpt 4 Lsn 8
Next Lesson
Percent yield
 Chemical equations and chemical analysis

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Chem 105 Chpt 4 Lsn 8
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Chem 105 Chpt 4 Lsn 8
p.162b
Balancing
Equations
____C3H8(g) + _____ O2(g) ---->
_____CO2(g) + _____ H2O(g)
____B4H10(g) + _____ O2(g) ---->
___ B2O3(g) + _____ H2O(g)
Chem 105 Chpt 4 Lsn 8
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