REVIEW – Ch. 8
Chemical Reactions
1. What are the indicators of a chemical
change?
• 1. gas produced
• 2. precipitate formed
• 3. changes color
• 4. evolution of heat and light
• 5. gets colder
2. State the Law of Conservation of Mass.
How does it apply to a chemical
equation? What else is balanced as a
result?
• Mass is neither created nor destroyed in
a chemical reaction.
• Mass of products = mass of reactants
• Number of atoms
3. Identify the symbols that compose a chemical
equation.
–
–
–
–
–
–
–
–
(s)
(aq)
+

(g)
(l)
Pt
- solid
- aqueous, dissolves in water
- plus, and
- produces, forms, yields
– gas
– liquid
– Platinum (Pt) used as a catalyst
– reactants must be heated
4. What is the difference between a
coefficient and a subscript?
3CO2
Coefficient – means 3
molecules of carbon dioxide
Subscript – means 2
oxygen atoms
5. List the 7 diatomic molecules.
•
Remember 7+1 on the periodic table
•
•
•
•
•
•
•
H2
N2
O2
F2
Cl2
Br2
I2
6. Define the following types of reactions:
– Synthesis – two or more substances
combine to form a new compound
– Decomposition – a single compound
undergoes a reaction that produces two or
more simpler substances
– Single Replacement – one element replaces
a similar element in a compound
– Double Replacement – the ions of 2
compounds exchange places in an aqueous
solution to form two new compounds
– Combustion – a substances combines with
oxygen, releasing a large amount of energy
in the form of heat and light
7. Balance the equations and identify them by
their type of reaction:
Single Replacement A. __2__ Li + __2__ HCl  __2__ LiCl + ___1__ H2
Double Replacement B. __1__ NiSO4 + _2__ NaI  __1__ NiI2 + __1__ Na2SO4
Synthesis
C. __2__ H2 + __1__ O2  __2__ H2O
Single Replacement D. __2__ Al + __1__ Fe2O3  __2_ Fe + __1__ Al2O3
Decomposition
Double Replacement
E. __2__ Al2O3  __4__ Al + __3__ O2
F. __1__ CaH2 + __2__ HNO3  __2__ H2 + __1__ Ca(NO3)2
Combustion
G. __1__ C4H8 + __6__ O2  __4__ H2O + __4__ CO2
Synthesis
H. ___1__ P4 + __5___ O2  __2__ P2O5
8. Define Activity Series. What does it
predict?
– A list of elements organized according to the
ease with which the elements undergo
certain chemical reactions
– Used to predict whether a single
replacement reaction will occur
9. What is the difference between an
element in the Activity Series at the top
and one at the bottom?
• Most reactive metal at the top, it will
replace any element below it.
• Least reactive element at the bottom, it
will not replace any element above it.
10. Predict what happens according to the
Activity Series:
• A. Fe + CuSO4→ FeSO4 + Cu
• B. Ni + NaCl → No Reaction
• C. Li + ZnCO3→ Li2CO3 + Zn
• D. Al + CuCl2→ AlCl3 + Cu
11. Exothermic or Endothermic?
– Reaction feels hot -
Exothermic / Endothermic
– Reaction feels cold - Exothermic / Endothermic
– Breaking bonds –
Exothermic / Endothermic
– Making bonds –
Exothermic / Endothermic
12. Find the molar masses of the following
compounds:
103 g/mol
1) NaBr
2) PbSO4
303 g/mol
3) Ca(OH)2
74 g/mol
4) Na3PO4
164 g/mol
13. Convert each of the following from grams
to moles:
1. 15.0 g C2H6
15.0 gC 2 H 6 1molC 2 H 6
 0.50molC2 H 6

1
30 gC2 H 6
140.0 gNaOH 1molNaOH

 3.50molNaOH
2. 140.0 g NaOH
1
40 gNaOH
3. 27.2 g H2O
4. 45.7 g CaCO3
27.2 gH 2O 1molH 2O
 1.51molH 2O

1
18 gH 2O
45.7 gCaCO3 1molCaCO3
 0.46molCaCO3

1
100 gCaCO3
14. Convert moles to grams in each of the
following:
1. 1.5 moles NH3
1.50molNH 3 17 gNH 3

1
1molNH 3
 25.5 gNH 3
2. 0.65 moles H2SO4
0.65molH 2 SO4 94 gH 2 SO4
 61gH2 SO4

1molH 2 SO4
1
15. Convert the following to moles:
1. 3.01 x 1023 atoms Na
1molNa
3.01x10 23 atomsNa

 0.50molNa
23
6.02 x10 atomsNa
1
2. 2.41 x 1024 molecules CO2
1molCO2
2.41x1024 moleculesC O2

 4.0molCO2
23
6.02 x10 moleculesC O2
1
16. Find the percent compositions of all of
the elements in the following compounds:
1)
CuBr2
2)
NaOH
3)
(NH4)2S
63.5 gCu
100  28.4%Cu
223.3gCuBr2
159.8 gBr
100  71.6% Br
223.3gCuBr2
23gNa
100  57.5% Na
40 gNaOH
16 gO
100  40.0%O
40 gNaOH
1gH
100  2.5% H
40 gNaOH
28 gN
100  41.1% N
68.1g ( NH 4 ) 2 S
8 gH
100  11.7% H
68.1g ( NH 4 ) 2 S
32 gS
100  47.0% S
68.1g ( NH 4 ) 2 S
17. Find the empirical formula for a compound
which contains 32.8% chromium and 67.2%
chlorine.
32.8 gCr 1molCr  0.63molCr / 0.63molCr  1

1
52 gCr
67.2 gCl
1molCl

 1.89molCl / 0.63molCr  3
1
35.5 gCl
EmpiricalF ormula  CrCl3
18. The percentage composition of acetic acid is
found to be 39.9% C, 6.7% H, and 53.4% O.
Determine the empirical formula of acetic acid.
39.9 gC 1molC

1
12 gC
 3.3molC
6.7 gH
1molH

1
1gH
53.4 gO 1molO

1
16 gO
 6.7molH / 3.3molC  2
/ 3.3molC  1
 3.3molO / 3.3molC  1
EmpiricalF ormula  CH2O
19. The molar mass for the question above (#18) was
determined by experiment to be 60.0 g/mol. What is
the molecular formula?
EmpiricalF ormula  CH2O
MolarMassC H 2O  30g / mol
MolarMassE xperimental
60 g / mol

2
MolarMassE mpiricalFo rmula 30 g / mol
2  CH2O  C2 H 4O2
MolecularF ormula  C2 H 4O2