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SCH 3U
Unit: Chemical Reactions
Unit Test Study Guide – Answer Key to Some of the Review Questions
b) Representing chemical equations, pg. 112 – 121. [page 117 #1, 2; page 155 #2, 3, 4, 10]
Pg. 117
1) Skeleton equations clearly show the correct formulas for all of the substances involved in a chemical reaction.
They do not show the correct ratios or relative numbers of atoms, molecules and ions.
2) (aq)
Pg. 155
2) CaCO3(s) 3) NaCl(aq) 4) answer is c
10) one
c) Write word equations and skeleton equations from a word description of a chemical reaction. [page 115
#1 – 10; page 117 #1, 3, 5, 6; page 121 #11; page 211 #28, 29]
Pg. 115
Word equation
Skeleton equation
Balanced chemical equation
Hydrogen(g) + oxygen(g)  water (g)
H2(g) +O2(g)  H2O(g)
2H2(g) +O2(g)  2H2O(g)
Sodium(s) + water(l) sodium hydroxide(aq) +
Na(s) + H2O  NaOH(aq) + H2(g)
2Na(s) + 2H2O  2NaOH(aq) + 2H2(g)
hydrogen(g)
Potassium chlorate(s)  potassium chloride(s) + KClO3(s)  KCl(s) + O2(g)
2KClO3(s)  2KCl(s) + 3O2(g)
oxygen(g)
Copper(s) + oxygen(g)  copper(II) oxide(s)
Cu(s) + O2(g)  CuO(s)
2Cu(s) + O2(g)  2CuO(s)
Silver nitrate(aq) + sodium chloride(aq) 
AgNO3(aq) + NaCl(aq)  NaNO3(aq) + AgNO3(aq) + NaCl(aq)  NaNO3(aq) +
sodium nitrate(aq) + silver chloride(s)
AgCl(s)
AgCl(s)
Pg. 117
3a) The correct chemical formulas and physical states of the reactants and products would be shown on the
appropriate sides of the arrow.
b) The relative numbers of each type of substance would not be shown in a skeleton equation.
5a) NaOH(aq) and H2(g) need to be corrected as shown. b) Na(s) + H2O  NaOH(aq) + H2(g)
6a) H2O(l)  H2(g) + O2(g) reactant is water; products are the 2 gases
b) Cl2(g) + ZnBr2(aq)  Br2(l) + ZnCl2(aq) reactants are to the left of the arrow, products to the right
pg. 121
11a) 2K(s) + Cl2(g)  2KCl(s) b) 2Al(s) + 3CuSO4(aq)  3Cu(s) + Al2(SO4)3(aq) c) N2(g) + 3H2(g)  2NH3(g)
d) CaCl2(aq) + F2(g)  CaF2(aq) + Cl2(g)
pg. 211
28 and 29 a) 2C6H6(l) + 15O2(g)  12CO2(g) + 6H2O(l) complete combustion of a hydrocarbon
b) CO(g) +O2(g)  CO2(g) can be classified as a synthesis reaction between a non-metal oxide and oxygen gas or a
combustion reaction
c) Cl2(g) + NaBr(s)  Br2(g) + NaCl(s) single displacement
d) CaCO3(s)  CaO(s) + CO2(g) decomposition of a carbonate
d) Balance chemical equations. [page 121 #10; page 155 #18, 19; page 159 #15]
Pg. 121
10. Changing a subscript alters the identity of the substance.
Pg. 155
18) see back of text 19) It may be that someone has chosen to “balance” the chemical equation by altering the
subscripts of reactants and/or products. Although the equation would appear to be balanced, altering the
subscripts will mean that the formulas for the reactants and products no longer match what actually appeared in
the chemical reaction.
Pg. 159 #15 – See answers in back of text.
e) Recognize synthesis, decomposition, combustion of a metal and incomplete and complete
combustion of a hydrocarbon [page 125 #9, 10, 12; page 159 #16; page 212 #42]
All of these questions have answers in the back of the textbook except for page 212 #42. So here is its answer:
i) decomposition – a compound is broken down into smaller parts; only one reactant is present
ii) synthesis – the opposite of decomposition in that 2 (or more) reactants come together to make (usually) one
product
iii) single displacement – one substance on its own displaces another substance that is originally part of a compound
iv) double displacement – the reactants are each made of two parts (often an anion and a cation) and the cations
change partners to produce two new compounds
e) Predict the products (if given the reactants) of chemical reactions that may be synthesis [pg. 127
#21 – 30 (answers in back of text); synthesis reactions of metal oxides and non-metal oxides and
water pg. 136 #7; page 210 #20, 21], decomposition [pg. 134 #31 – 40 (answers in back of text);
decomposition products of nitrates, carbonates and hydroxides, read pg. 130 “Types of
Decomposition Reactions”; page 134 #31 – 40 (answers in back of text); page 156 #21 (answers in back
of text); page 210 #13, 14; page 212 #48], combustion of metals [page 145 #15] and incomplete and
complete combustion of hydrocarbons [page 141 #41 – 50 (answers in back of text);
pg. 143 #25, 26 (answers in back of text); pg. 210 #24] Also page 210 #16 (answers in back of text), 17,
18, 25, 26 (answers in back of text),
Pg. 136
7) non-metal oxides form acids in water and metal oxides form bases
a) acid b) base c) acid d) base
pg. 210
13a) decomposition of a carbonate b) decomposition of a compound c) decomposition of a nitrate
14) Decomposition as the electrical energy is used to break a compound up into its elements.
17a) decomposition b) synthesis and combustion c) complete combustion of a hydrocarbon d) decomposition
18a) single displacement b) combustion and synthesis c) decomposition d) synthesis e) double displacement
f) decomposition
20) non-metal oxides form acids in water and metal oxides form bases
a) base (BaOH) b) acid (H3PO4) c) acid (H2CO3) d) base (LiOH)
21) a non-metal oxide
24) The flame showing complete combustion is on the right. It is a stronger, blue-white flame indicating lots of
oxygen is present and the fuel is burning completely. The weak yellow flame indicates lack of oxygen gas so the
fuel is undergoing incomplete combustion.
25a) oxygen gas is produced as it is the gas that supports burning (combustion)
b) It is a decomposition reaction as there is only one reactant and it is being heated to break it up.
c) The mass will decrease unless the oxygen gas is somehow prevented from escaping the reaction container.
Pg. 212
48a) You could decompose magnesium carbonate to generate magnesium oxide or you could decompose
magnesium hydroxide to generate magnesium oxide.
b) MgCO3(s)  MgO(s) + CO2(g) or Mg(OH)2(aq)  H2O(l) + MgO(aq)
Pg. 145
15a) both – because the metal is burning in oxygen (combustion) and two smaller compounds are forming a larger
one (synthesis)
b) complete combustion of a hydrocarbon
c) synthesis reaction – two elements are reacting together to make a single compound
g) Use an activity series to predict whether or not a given single displacement reaction will
occur. If the reaction does occur, you should be able to predict its products and, with some
certainty, the physical states of those products. [page 165 #5, 6 (answers in back of text); page 169
#1 -10 (answers in back of text); page 170 #4, 5 (answers in back of text), 7, 10, 12 (answers in back of
text), 13, 14; page 209 #5, 6 (answers in back of text), ]
h) Use a solubility table to predict whether or not a given ionic compound is reasonably water
soluble and/or whether or not a double displacement reaction involving the production of a
precipitate is a possibility. [page 175 #11 – 20 (answers in back of text); page 177 #17 (answers in back
of text); page 201 #4, 5 (answers in back of text); page 211 #32 (answers in back of text), 34; page 212
#43
Pg. 211-212
34) Lead (II) sulfate will be a precipitate if you add sulfate ions to the solution. Similarly, silver chloride will
precipitate out if chloride ions are added to the mixture. So, add one of these ions in, then filter off the
precipitate. Then add the other ion and isolate the second precipitate.
43) Predicting whether or not a single displacement reaction will occur requires one to know which element is the
more reactive – the one on its own or the one in a compound. Predicting whether a double displacement
reaction involving the formation of a precipitate will occur involves knowing whether each of the two potential
ionic compounds that might be produced is or is not reasonably water soluble. If one of them is reasonably
insoluble, it can be predicted that the d.d. reaction will occur. For these reasons, single displacement reactions
require the use of an activity series and double displacement reactions require consulting a solubility table.
i) Review the other two possible types of double displacement reactions: acid – base neutralization
and formation of a gas. [page 177 #16 (answers in back of text); page 179 #21 – 30 (answers in back of
text); page 201 #2, 7 (answers in back of text); page 211 #33,
Pg. 211
33a) acid and a base b) an aqueous salt and liquid water c) boil off the water, recover the salt and test it for the ions
you predict should be present (using a flame test, for example)
j) Review the gas tests we have to test various reaction products in this unit. The gas tests are
covered in the 10 station lab we do in this unit. If we have not completed the lab work by test day,
the gas tests will be covered in an evaluation later in the course.