#42 The equation for the formation of water
from its elements,
H2 (g) + O2(g)  H2O(l) can be “balanced”
by changing the formula of the product to
H2O2. Explain why this is incorrect.
To change the subscripts like that
actually changes the product to a
totally different one. You cannot
touch the subscripts to “balance” the
equation, only add coefficients.
#43. Balance the following equations:
a. 2 PbO2  2 PbO + O2
b. 2 Fe(OH)3 
c.
Fe2O3 + 3 H2O
(NH4)2CO3  2 NH3 + H2O + CO2
d. 2 NaCl +
H2SO4 
Na2SO4 + 2 HCl
#44 What is a characteristic of every
combination reaction?
Every combination reaction has a
single product. example:
2H2 + O2  2H2O
single product
#45 Write balanced chemical equations
for the following combination reactions.
a. 2 Mg +
O2

2MgO
b. P + O2  diphosphorous pentoxide
4P + 5O2  2P2O5
c. Ca + S 
CaS
#46 What is a distinguishing feature of
every decomposition reaction?
a decomposition always has a single
reactant. example:
2H2O  2H2 + O2
#47 Write a balanced chemical
equation for each decomposition
reaction:
a. 2 Ag2O(s)  4 Ag
b.
+ O2
ammonium nitrate  dinitrogen monoxide
NH4NO3 
N2O
+ water
+ 2H2O
#48 Use the activity series of metals
to write a balanced equation for each
single-replacement reaction.
a.
b.
Au(s)
NO reaction. K is
higher on the chart
than Au
+ KNO3
Zn(s) + 2AgNO3  Zn(NO3)2(s)
c. 2 Al(s)
+ 3H2SO4

Al2(SO4)3
+2Ag
+ 3 H2
#49 write a balanced equation
for each of the following doublereplacement reactions.
a.
H2C2O4(aq) + 2KOH(aq) 
2H2O
b.
+
K2C2O4
CdBr2(aq) + Na2S(aq) 
CdS
+
2NaBr
#50 What is common to all combustion
reactions?
oxygen on the left side
example:
C4H8
+
6O2

4CO2
+
4H2O
#51 Write a balanced equation for
the complete combustion of each
compound.
a. Butene (C4H8)
C 4H 8
+
6O2

4CO2
+
4H2O
b. acetone (C3H6O)
C 3H 6O
+
4O2

3CO2
+
3H2O
#52 Balance each equation and identify
its type.
a. 3 Hf + 2 N2

Hf3N4
a combination reaction
b.
Mg +
H2SO4

MgSO4 + H2
a single-replacement reaction
c. 2 C2H6 + 7 O2
 4 CO2 +6 H2O
a combustion
#52 Balance each equation and identify
its type.
continued….
d.
Pb(NO3)2 + 2 NaI
 PbI2 + 2 NaNO3
a double-replacement reaction
e. 4 Fe
+ 3 O2
 2 Fe2O3
a combination reaction