Chapters 6 – 7
Chemical Reactions
Evidence for a Chemical Reaction
Change in Color
Hair changes color when it is bleached
A blue flame appears when natural gas reacts with oxygen
Formation of a Precipitate (Solid)
A yellow solid forms when a solution of KI reacts with Pb(NO3)2
Nylon is formed when two particular liquid solutions are combined
Production of Gas
Bubbles of hydrogen gas form when calcium metal reacts with water
H2 and O2 gas form when an electric current is used to decompose water
Heat / Light is Produced – Heat is Absorbed
A bright white flame is produced when magnesium metal burns
Oxygen from the air penetrates the solid chemicals in the pouch of foot
warmers – the reaction produces heat for several hours
Chemical Equations
- any change in which one or more
substances are converted into different substances with
different characteristic properties
Reactants –
Products –
Reactants → Product
http://www.youtube.com/watch?v=Mx5JJWI2aaw
Writing Chemical Equations
Chemical Equation -
Chemical Equations Contain Useful Information
Formulas – the reactants and products are written with their correct
chemical formulas
Phases – a symbol which expresses the state of the substance, is often
included to the right of the formula (written in parentheses)
Amounts – relative numbers of reactant and product molecules that are
required (coefficients)
Sample Chemical Reaction
Balancing Chemical Equations
Conservation of Matter
•Matter cannot be created or destroyed.
•In a chemical reaction, all the atoms present
at the beginning are still present at the end.
•Reactions involve rearrangement and
exchange of atoms to produce new
molecules.
•The total mass cannot change.
CH4 (g) + 2 O2 (g)
CO2 (g) + 2 H2O (l)
Balancing Chemical Equations

LiNO3
BaO
+
LiNO2
P2O5
+

CaCO3

MnSO4
+
K3PO4
Al(OH)3
+
H2SO4
C8H18
SiF4
+
+
CaO
+
O2
Ba3(PO4)2
CO2


Mn3(PO4)2
+
K2SO4
Al2(SO4)3
+
H2O
O2

CO2
H2O

H2SiF6
+
H2O
+
H2SiO3
Types of Reactions
Synthesis (Combination) –
The starting materials can be elements or
compounds but the product must be a
compound.
2 Na + Cl2 → 2 NaCl
H2 + F2 → 2 HF
MgO + H2O → Mg(OH)2
Types of Reactions
Decomposition –
2 Al2O3 → 4 Al + 3 O2
2 KNO3 → 2 KNO2 + O2
The starting material must be a compound. The products can
be either elements or compounds.
Decomposition reactions require energy:
Types of Reactions
Single-Replacement –
-reactants and products always include one
element and one compound
2 Al + 3 Fe(NO3)2 → 3 Fe + 2 Al(NO3)3
F2 + 2 HCl → 2 HF + Cl2
Halogens
fluorine
chlorine
bromine
iodine
Predict the products of the following singlereplacement reactions. If no product exist write NAR
for no apparent reaction.
Zn(s) + HCl(aq) →
Na(s) + H2O(l) →
Sn(s) + AlCl3(aq) →
Cu(s) + AgNO3(aq) →
F2(g) + HBr(aq) →
Types of Reactions
Double-Replacement –
One of the products must be a:
Pb(NO3)2 (aq) + 2 KI (aq) → PbI2 (s) + 2 KNO3 (aq)
FeS (s) + 2 HCl (aq) → H2S (g) + FeCl2 (aq)
HCl (aq) + NaOH (aq) → NaCl (aq) + H2O (l)
Double Replacement Reactions
How do you know if a precipitate forms?
One or more of the products must be insoluble in water
(this means that the substance does NOT dissolve in
water).
Learn and use the KISS Guidelines!!!
Keep It Simple Solubility
KISS Guidelines
All salts containing (insert any ion from Guidelines 1-4)
are soluble
Cation Guideline:
1. Na+, NH4+, K+
Anion Guidelines:
2. NO3-, C2H3O2-, ClO3-, ClO43. Halides (Cl-/Br-/I-) except when paired with Ag+,
Hg22+, Pb2+
4. SO42- except when paired with Ag+, Hg22+, Pb2+,
Ba2+ and Sr2+
The “Catch-all” Guideline:
5. Everything else is assumed to be insoluble.
Soluble or Insoluble?
manganese(II) chloride
lead(II) sulfate
potassium fluoride
magnesium sulfate
sodium carbonate
chromium(III) hydroxide
ammonium sulfide
zinc(II) phosphate
silver(I) chloride
Predict the identity of the precipitate that forms when
aqueous solutions of the following substances are mixed.
If no precipitate is likely, indicate which rules apply.
FeCl3 + H3PO4 →
K2SO4 + Ca(C2H3O2)2
Na2CO3 + MnCl2
KOH + NiCl2
→
→
→
→
Ba(NO3)2 + H2SO4 →
AgNO3 + CaBr2 →
(NH4)2S + MgCl2
Double Replacement Reactions
How do you know if a gas forms?
Learn the following compounds and recognize them as gases or
“phantom” gases.
hydrogen sulfide – H2S (g)
hydrogen cyanide – HCN (g)
carbonic acid – H2CO3
sulfurous acid – H2SO3
ammonium hydroxide – NH4OH
Predict the products of the following reactions.
HCl (aq) + K2SO3 (aq)
→
NaOH (aq) + NH4Cl (aq)
HCl (aq) + Na2S (aq)
→
→
H2SO4 (aq) + KCN (aq)
→
HCl (aq) + NaHCO3 (aq)
→
Double Replacement Reactions
Acid-Base Reactions
Neutralization Reactions
The products of an acid-base reaction are
STRONG ACID + STRONG BASE
→ HOH + “salt”
HCl + NaOH → HOH + NaCl
A “salt” is defined as an ionic compound.
Acids
• Acid comes from the Latin word “acidus” which means
sour.
• In the 1800’s, Svante Arrhenius discovered the essential
nature of acids.
– He observed that when the substances HCl, HNO3, and H2SO4
were dissolved in water, they behaved as strong electrolytes
(they conducted electricity well)
– He suggested that this was the result of ionization.
HCl + H2O → H+ (aq) + Cl- (aq)
HNO3 + H2O → H+ (aq) + NO3- (aq)
H2SO4 + H2O → H+ (aq) + HSO4- (aq)
Strong Acids
Strong acids –
Learn the following strong acids.
Bases
• Arrhenius also found that aqueous solutions that
exhibit basic behavior always contain hydroxide
ions (OH-).
• Learn the strong bases:
Acid-Base Reactions
Strong Acid + Strong Base
HBr(aq) + NaOH(aq)
→
HNO3(aq) + KOH(aq)
→
Ba(OH)2(aq) + HCl(aq)
→
→
Water + A “salt”
HOH(l) + NaBr(aq)
Combustion
Reactions
Combustion –
-the burning of natural gas, wood, and
propane are examples
-when hydrocarbons burn completely, they
form carbon dioxide and water
-hydrocarbons are compounds composed
of carbon and hydrogen
Methane
Ethane
Propane
Butane
Pentane
Hexane
Heptane
Octane
Nonane
Decane
C3H8 (g) + O2 (g) → CO2 (g) + H2O (g)
CH4 (g) +
O2 (g) → CO2 (g) + H2O (g)
CH4
C2H6
C3H8
C4H10
C5H12
C6H14
C7H16
C8H18
C9H20
C10H22