chemical equation balancing chemical equation types of chemical equation

1. Chapter 7:
Chemical
Equations and
Reactions

2. 7.1 Chemical Equation
7.2 Balancing Chemical
Equations
7.3 Information Obtained
From a Balanced
Equation
7.4 Types of Chemical
Reactions

3. 7.1 Chemical Equation
• Is a shorthand expression for a chemical
change or reaction.
• Reactants – the substance entering the
reaction.
• Products – is the substance formed.
• During a chemical reaction, atoms, molecules,
or ions interact and rearrange themselves to
form the products.
• During the process chemical bonds are broken
and new bonds are formed.
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4. 4

5. 5

6. 7.2 Balancing Chemical Equations
• Balanced Equation – contains the same
number of each kind of atom on each
side of the equation.
• Obeys the Law of Conservation of Mass
• Example :
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7. Pointers in balancing chemical equations
• Set up the equation which
shows the correct formulas of
all reactants and products.
(diatomic elements can stand
alone – H2,O2,N2,F2,Cl2,Br2 &I2)
• Start balancing elements that
appear only once in each side
of the equation but in an
unequal numbers of atom.
Balanced each elements, one
at a time by placing whole
number coefficients in front of
the formulas containing the
unbalanced element. A
coefficients multiplies every
atom in the formula by that
number.
• Ex. 2H3PO4
• Balance polyatomic ions as a
group when they appear
unchanged on both sides of the
equation.
• Use the smallest possible set of
coefficients that will give the
same number of atoms of the
elements on both sides of the
equations.
• A subscript should never be
changed while balancing an
equation.
• Convert a fractional coefficient
into a whole number by
multiplying the entire equation
by the appropriate integer.
• Check each element or
polyatomic ion is balanced.
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8. • Example 7.1 Write the balanced equation for the
reaction that takes place when magnesium metal is
burned in air to produce magnesium oxide.
 Write the formula equation
Mg + O2 MgO
 Start balancing the O atoms since there are two O
atoms on the left side and one on the right side.
Mg + O2 2MgO
 Mg is not balanced.
2Mg + O2 2MgO
 Check: Each side has two Mg and two O atoms.
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9. • Example 7.2 Calcium chloride and iron (III) sulfate
solutions react to form a precipitate of calcium sulfate
and iron (III) chloride solution. Write the balanced
equation for this reaction.
 Write the formula equation.
CaCl2 + Fe2(SO4)3  CaSO4 + FeCl3
3CaCl2 + Fe2(SO4)3  CaSO4 + 2FeCl3
3CaCl2 + Fe2(SO4)3  3CaSO4 + 2FeCl3
 Check the equation
Reactant Product
3 Ca 3
6 Cl 6
2 Fe 2
3 S 3
12 O 12
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10. • Example 7.3 When butane gas undergoes complete
combustion, it reacts with oxygen to form carbon
dioxide and water. Write the balanced equation for this
reaction.
• C4H10 + O2  CO2 + H2O
• C4H10 + O2  4 CO2 + H2O
• C4H10 + O2  4 CO2 + 5 H2O
• C4H10 + 6 ½ O2  4 CO2 + 5 H2O
• C4H10 + 13 O2  4 CO2 + 5 H2O
Reactant Product
8 C 8
20 H 20
26 O 26
10

11. Exercise 7.1 Balancing Chemical Equations
A. Formulate and balance the following word equations
1. Tetraphosphorus decoxide + water  phosphoric acid
P4O10 + H2O  H3PO4
2. Zinc sulfate heptahydrate  zinc sulfate + water
ZnSO4 7H2O  ZnSO4 + H2O
3. Silver nitrate + sodium chromate  silver chromate + sodium nitrate
AgNO3 + Na2CrO 4  Ag2CrO4 + NaNO3
4. Aluminum + copper (II) nitrate  aluminum nitrate + copper
Al + Cu(NO3)2  Al(NO3)3 + Cu
5. Lead (II) oxide + ammonia  lead + nitrogen + water
PbO + NH3  Pb + N2 + H2O
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6 4
7
22
33 22
323 3

12. B. Balance the following chemical equations
1. Mg + HCl  MgCl2 + H2
Mg + 2HCl  MgCl2 + H2
2. NaOH + H2SO4  Na2SO4 + H2O
2NaOH + H2SO4  Na2SO4 + 2H2O
3. Na2SO3 + S  Na2S2O3
balanced already
4. NaCl  Na + Cl2
2NaCl  2Na + Cl2
5. C + S2Cl2  CCl4 + S
C + 2S2Cl2  CCl4 + 4S 12

13. 7.3 Information Obtained From a
Balanced Equation
• Consider the equation
2 Na (s) + Cl2 (g)  2 NaCl (s)
2 Na Cl2 2 NaCl
2 atoms 1 molecule 2 formula units
2 moles 1 mole 2 moles
45.98 g 70.9 g 116.88 g
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14. 7.4 Types of Chemical Reactions
• COMBINATION REACTION
In a combination reaction, two reactants combine
to give a single products. The general form of the
equation is
A + B  AB
* where A and B are either elements or compounds
and AB is a compound that fall into this category are
the following:
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15. • Metal + Oxygen  Metal Oxide
ex. Al + 3O2  2Al2O3
• Nonmetal + Oxygen  Nonmetal Oxide
ex. C + O2  CO2
• Metal + Nonmetal  Salt
ex. 2Fe + 3Br2  2FeBr3
• Metal Oxide + Water  Base
ex. Li2O + H2O  2LiOH
• Nonmetal Oxide + H2O  Oxyacid
ex. P2O5 + 3H2O  2H3PO4
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16. • Let’s try this!
• 1. Predict the product formed from the
following combination reaction:
a. Si + N2  ___________
b. Al + Br2  ________________
c. MgO + H2O  ____________
d. Cs + Br2  _______________
e. Cu + O2  ______________
SiN2
AlBr3
Mg(OH)2
CsBr
Cu2O
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232
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17. •DECOMPOSITION REACTION
In a decomposition reaction a single reactant is
decomposed or broken down to give two or more
different products. The general form of the equation is
…
AB  A + B
in which AB is a compound and A and B are either
elements or compounds. Many compounds undergo
decomposition reactions when heated; some, when
passed through electric current (electrolysis).
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18. The following are decomposed by heating
• metal oxides  metal + oxygen
ex. 2HgO  2Hg + O2
• Most carbonates (except 1A)  oxide + carbon dioxide
ex. CaCO3  CaO + CO2
• Group 1A bicarbonates  carbonate + carbon dioxide + water
ex. 2NaHCO3  Na2CO3 + CO2 + H2O
• Other bicarbonates  oxide + carbon dioxide + water
ex. Mg(HCO3)2  MgO + 2CO2 + H2O
• Hydrates  anhydrous salt + water
ex. CuSO45H2O  CuSO4 + 5H2O
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19. • Chlorates  chloride + Oxygen
ex. 2KClO3  2KCl + 3O2
• Nitrates  nitrite + oxygen
ex. 2NaNO3  2NaNO2 + O2
• Peroxides  oxide + oxygen
ex. 2Na2O2  2Na2O + O2
Water and some salts are compounds that are
decomposed by electrolysis
2H2O  2H2 + O2
2NaCl  2Na + Cl
electrolysis
electrolysis
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20. • Let’s try this!
• Predict the products formed from the following
decomposition reactions.
a. SiH4  ________________
b. H2O2  _________________
c. BaCO3  _______________
d. CaSO4  2H2O  _____________
e. KHCO3  __________________
Si + H2
H2O + O2
BaO + CO2
CaSO4 + H2O
K2CO3 + CO2 + H2O
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2
22
2

21. • DISPLACEMENT REACTION
• In a displacement reaction one free element reacts
with a compound to replace one of the elements of that
compound. A different element and a different
compound are formed. Most displacement reactions fit
into one of three subcategories:
» Metal displacement
» Hydrogen displacement
» Halogen displacement
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22. A. Metal Displacement
• In a metal displacement reaction, a more reactive
metal replaces a less reactive metal from its
compound. The general form equation is :
A + BC  B + AC
In which A and B are both metals. A will displace B
from BC, providing A is a more reactive metal
than B.
The activity series for selected metals and their
degree of reactivity are shown in Table 7.1. We
describe the metals as highly reactive, slightly
reactive, and unreactive based on their ability to
displace hydrogen gas from an acid and water.
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23. 23

24. B. Hydrogen displacement
• the metals, depending on their reactivity, will
displace hydrogen gas from acids and water. The
metals reacts as follow:
 All metals above H (from Li to Pb) in the activity series
will displace hydrogen from acid.
Mg + 2HCl  H2 + MgCl2
 The highly reactive metals Li, Ba, Ca, and Na will
displace hydrogen from water even at room
temperature.
2Na + 2H2O(l)  H2 + 2NaOH
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25.  The moderately reactive metals Mg, Al, Zn, Cr, and Fe
will displace hydrogen only from steam or hot water.
2Al + 3H2O(g)  3H2 + Al2O3
 The slightly reactive metals Cd, Co, Ni, Sn and Pb will
displace hydrogen from an acid but not water.
 The unreactive metals Cu, Hg, Ag, Pt and Au will not
displace H2 gas from an acid or water.
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26. C. Halogen Displacement
• For the halogens, the most reactive is fluorine,
followed by chlorine, bromine, and iodine in
decreasing order. As in metal displacement, a
more reactive halogen will displace a less
reactive one from its compound. The general
from of equation is:
A + BC  C + BA
in which A and C are both halogens. A will displace
C from BC, providing A is a more reactive halogen
from C.
Example:
Cl2 + 2NaBr  Br2 + 2NaCl
Br2 + 2KI  I2 + 2KBr
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27. Let’s Try This!
Predict the products formed, if any, from the following
displacement reactions:
1. Au + Ag2O  ______________
2. Zn + Fe(NO3)3  ______________
3. KF + Cl2  ________________
4. PbO2 + Ca  ______________
5. Al + SnCl2  ______________
No reaction
Fe + Zn(NO3)3
No reaction
CaO2 + Pb
Sn + AlCl2
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28. • DOUBLE DISPLACEMENT
In a double displacement reaction, two compounds
exchange component ions with each other to produce
two new compounds. The general form of equation is
AB + CD  AD + CB
this reaction may be described as an exchange of
positive and negative components, where A combines
with D and C combines with B. Reaction occurs when
one of the following products are formed:
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29. 1. Water
H2SO4 + 2NaOH  Na2SO4 + H2O(l)
2. A precipitate
Na2SO4 + BaCl2  BaSO4(s) + 2NaCl
3. A gas
MgS + 2HCl  MgCl2 + H2S(g)
4. A weak electrolyte, such as H2CO3 and NH4OH. These
products, however, are unstable enough to decompose
further into CO2 + H2O, SO2 + H2O and NH3 + H2O,
respectively. To illustrate,
 K2CO3 + H2SO4 K2SO4 + H2CO3 K2SO4 + CO2(g) + H2O
 Na2SO3 + 2HNO3 2NaNO3 + H2SO3 2NaNO3 + SO2(g) + H2O
 NaOH + NH4Cl  NaCl + NH4OH  NaCl + NH3(g) + H2O
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30. Let’s Try This!
Predict the products formed from the following double
displacement reactions:
1. 3HCl + 3Al(OH)3  _______________________
2. 2BaCl2 + (NH4)2SO4  _______________________
3. Mg(NO3)2 + K3PO4  ________________________
4. Li2CO3 + CaCl2  ____________________________
5. K2SO3 + HCl  ______________________________
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3H2O + 3AlCl
Mg(NO3)2 + K3PO4
2LiCl + CaCO3
KCl + H2SO4  KCl + SO4 + H2O
2Ba2SO4 + 4NH4Cl

31. Exercise 7.3 Types of Chemical Reactions
• Classify the following into combination,
decomposition, displacement or double displacement
1. CO + 2H2 CH3OH ___________________
2. 2Al + 3H2O  Al2O3 + 3H2 _______________
3. Al(OH)3 + 3HCl  AlCl3 + 6H2O ______________
4. Br2 + 2KI 2KBr +I2 ___________________
5. 2NaClO3  2NaCl + 3O2 __________________
6. 6Li + N2  2Li3N ______________________
7. MgSO4  7H2O  MgSO4 + 7H2O ______________
8. 2NO  N2 + O2 ___________________
9. 2Ag + PtCl2  2AgCl + Pt ________________
10.2HClO4 + Mg(OH)2  Mg(ClO4)2 + 2H2O __________
Combination
Displacement (hydrogen)
Double Displacement
Displacement (halogen)
Decomposition
Combination
Decomposition
Decomposition
Displacement (Metal)
Double Displacement 31

32. …..for listening and for your cooperation 
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