Transcript Balancing Equations

Balancing Equations
Balancing, Writing, and Naming
Equations
Balancing Equations
Balancing Equations

Law of Conservation
of Matter:
In a chemical reaction,
matter can be neither
created nor destroyed.
 In a chemical reaction,
the amount of
reactants equal the
amount of products.
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Balancing Equations
Paraphrase:
 Law of Conservation of
Atoms:
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The number of atoms of
each type of element
must be the same on
each side of the
equation.
Balancing Equations
 Hydrogen
 H2
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+ oxygen
+ O2
water
H2O
Hydrogen and oxygen are diatomic
elements.
Their subscripts cannot be changed.
The subscripts on water cannot be
changed.
Balancing Equation
 H2

+ O2
H2O
Count the atoms on each side.
Reactant side: 2 atoms H and 2 atoms
O
 Product side: 2 atoms H and 1 atom O
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Balancing Equations
 H2
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
+ O2
H2O
If the subscripts cannot be altered,
how can the atoms be made equal?
Adjust the number of molecules by
changing the coefficients.
Balancing Equations
 H2
+ O2
2H2O
Reactants: 2 atoms of H and 2 atoms
of O
 Products: 4 atoms of H and 2 atoms
of O
 H is no longer balanced!
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Balancing Equations
 2H2
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+ O2
2H2O
Reactant side: 4 atoms of H and 2 atoms
of O
Product side: 4 atoms of H and 2 atoms
of O
It’s Balanced!
Balancing Equations
 N2
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+ H2
Nitrogen + hydrogen
NH3
ammonia
Count atoms.
Reactants: 2 atoms N and 2 atoms H
 Products: 1 atom N and 3 atoms of NH3
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Balancing Equations
Nothing is balanced.
 Balance the nitrogen first by placing a
coefficient of 2 in front of the NH3.
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 N2
+ H2
2NH3
Balancing Equations
Hydrogen is not balanced.
 Place a 3 in front of H2.
 Reactant side: 2 atoms N, 6 atoms H
 Product side: 2 atoms N, 6 atoms H
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 N2
+ 3H2
2NH3
Balancing Equations

Ca3(PO4)2 + H2SO4
CaSO4 + H3PO4
Count atoms.
 Reactants: Ca – 3 atoms, P – 2
atoms, O – 8 atoms; H – atoms, S – 1
atom, O – 4 atoms
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Balancing Equations
 Side
note on Ca3(PO4)2
The subscript after the phosphate
indicates two phosphate groups.
 This means two PO43- groups with
two P and eight O atoms.
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Balancing Equations
 Ca3(PO4)2
+ H2SO4
CaSO4 + H3PO4
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Count atoms in the product.
Ca atoms – 1, S atom – 1, O atoms – 4; H
atoms – 3, P atom – 1, O atoms - 4
Balancing Equations
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In this equation, the ion groups do not
break up.
Instead of counting individual atoms, ion
groups may be counted.
 Ca3(PO4)2
+ H2SO4
CaSO4 + H3PO4
Balancing Equations
 Ca3(PO4)2
+ H2SO4
CaSO4 + H3PO4
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Reactants: Ca2+ – 3, PO43- - 2, H+ – 2,
SO42+ - 1
Products: Ca2+ - 1, SO42- - 1, H+ - 3, PO43-1
Balancing Equations
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Balance the metal first by placing a
coefficient of 3 in front of CaSO4.
Products: Ca – 3 atoms, SO42- - 3 groups
 Ca3(PO4)2
+ H2SO4
3CaSO4 + H3PO4
Balancing Equations
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Three sulfate groups are needed on the
reactant side so place a coefficient of 3 in
front of H2SO4.
3H2SO4 gives 6 H+ and 3 SO42-.
Neither phosphate nor calcium is
balanced.
 Ca3(PO4)2
+ 3H2SO4
3CaSO4 + H3PO4
Balancing Equations
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A coefficient of 2 placed in front of
H3PO4 which balances both hydrogen
and phosphate.
 Ca3(PO4)2
+ 3H2SO4
3CaSO4 + 2H3PO4
Balancing Equations
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Cu + H2SO4
CuSO4 + H2O + SO2
The sulfate group breaks up. Each atom
must be counted individually. Ugh!
Reactants: Cu – 1, H – 2, S – 1, O – 4
Products: Cu – 1, S – 1, O - 4, H – 2, O –
1, S – 1, O - 2
Balancing Equations
Sulfur is not balanced.
 Place a two in front of sulfuric acid.
 Count atoms: 2 H2SO4 H – 4, S – 2,
O-8
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Cu + 2H2SO4
 CuSO4 + H2O + SO2
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Balancing Equations
Hydrogen needs to be balanced so
place a 2 in front of the H2O.
 Count the number of atoms.
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Cu + 2H2SO4
 CuSO4 + 2H2O + SO2
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Balancing Equations
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Reactants: Cu – 1, H – 4, S – 2, O – 8
Products: Cu – 1, S – 1, O – 4, H – 4, O –
2, S – 1, O – 2 = Cu – 1, S – 2, H – 4, O
–8
 It’s balanced!
Cu + 2H2SO4
 CuSO4 + 2H2O + SO2
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Balancing Equations
 Balancing
 Balance
hints:
the metals first.
 Balance the ion groups next.
 Balance the other atoms.
 Save the non ion group oxygen and
hydrogen until the end.
Balancing Equations
This method of
balancing
equations is the
inspection
method.
 The method is
trial and error.
 Practice.
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Writing and Naming
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Nickel + hydrochloric acid
Nickel(II) chloride + hydrogen
Write the corresponding formula
equation and then balance the
equation.
Writing and Naming
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Write each formula independently.
Ignore the rest of the equation.
Balance the equation after writing the
formulas.
Ni + HCl
NiCl2 + H2
Ni + 2HCl
NiCl2 + H2
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Writing and Naming
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Remember the diatomic elements: H2, N2,
O2, F2, Cl2, Br2, and I2.
Writing and Naming
Cu + H2SO4
 CuSO4 + H2O + SO2
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Balance the formula equation.
 Write the word equation.
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Writing and Naming
Cu + 2H2SO4
 CuSO4 + 2H2O + SO2
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Write the names:
Cu by itself is just copper. Copper(I) or
copper(II) would be incorrect.
H2SO4 should be named as an acid.
Sulfuric acid
Writing and Naming

CuSO4 has a SO42- group so Cu must
be 2+. Some metals must have
Roman Numerals. Copper(II)
sulfate
H2O is known as water.
 SO2 is a nonmetal compound. Its
name is either sulfur dioxide or
sulfur(IV) oxide.
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Writing and Naming
Cu + 2H2SO4
 CuSO4 + 2H2O + SO2
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Copper + sulfuric acid 
 Copper(II) sulfate + water + sulfur
dioxide
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Balancing Equations
 Practice!
 Practice!
 Practice!