1. To change the subscripts like that actually changes the product to a
#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.

2. #43. Balance the following equations:
a. PbO2  PbO + O2 2 2
b. Fe(OH)3  Fe2O H2O 2 3
c. (NH4)2CO3  NH H2O + CO2 2
d. NaCl H2SO4  Na2SO HCl 2 2

3. single product Every combination reaction has a
#44 What is a characteristic of every
combination reaction?
Every combination reaction has a
single product. example:
2H O2  2H2O
single product

4. #45 Write balanced chemical equations
for the following combination reactions.
a. Mg O2  2
2MgO
b. P + O2  diphosphorous pentoxide
4P + 5O2  2P2O5
c. Ca + S 
CaS

5. a decomposition always has a single reactant. example:
#46 What is a distinguishing feature of
every decomposition reaction?
a decomposition always has a single
reactant. example:
2H2O  2H O2

6. #47 Write a balanced chemical equation for each decomposition
reaction:
Ag O2
a. Ag2O(s)  4 2
b. ammonium nitrate  dinitrogen monoxide
+ water
NH4NO3  N2O H2O

7. #48 Use the activity series of metals
to write a balanced equation for each
single-replacement reaction.
NO reaction. K is
higher on the chart
than Au
a. Au(s) KNO3
b Zn(s) AgNO3  2
Zn(NO3)2(s) Ag 2
c Al(s) H2SO4  2 3
Al2(SO4) H2 3

8. #49 write a balanced equation
for each of the following double-
replacement reactions.
a. H2C2O4(aq) KOH(aq) 
2H2O K2C2O4
b. CdBr2(aq) Na2S(aq) 
CdS NaBr

9. oxygen on the left side #50 What is common to all combustion
reactions?
oxygen on the left side
example:
C4H O2  CO H2O

10. #51 Write a balanced equation for the complete combustion of each
compound.
a. Butene (C4H8)
C4H O2  CO H2O
b. acetone (C3H6O)
C3H6O O2  CO H2O

11. #52 Balance each equation and identify its type.
a. Hf N2  Hf3N4 3 2
a combination reaction
b. Mg H2SO4  MgSO H2
a single-replacement reaction
c. C2H O2  CO H2O 2 7 4 6
a combustion

12. #52 Balance each equation and identify its type. continued….
d. Pb(NO3) NaI  PbI NaNO3 2 2
a double-replacement reaction
e. Fe O2  Fe2O3 4 3 2
a combination reaction