Unit 4Notes
CHEMICAL REACTIONS AND EQUATIONS
Unit 5 Notes: Part 1 Types of Reactions
 Chemical Reactions occur when bonds between
atoms are formed or broken.
 Indications that a chemical reaction has occurred:
 Color change
 Gas production (bubbles)
 Precipitate formed (solid formed from 2 liquids)
 Temperature change
Indications that a chemical reaction has
occurred:
 Gas production:
 http://www.youtube.com/watch?v=rjprBJAZECM&safe=activ
e
 Precipitate:
 http://www.youtube.com/watch?v=8RmVwz2fNGc
&safe=active
 Temperature change:

http://www.youtube.com/watch?v=RhQM4DHV4c&safe=active
 Color change (precipitate):
 http://www.youtube.com/watch?v=pFovlKpPCbI&safe=active
What is a chemical equation?
 Chemical Symbols: represent elements: Mg, S
 Chemical Formulas: represent compounds: MgS
 Chemical Equations: represent reactions:
Mg + S
MgS
(reactants) (products)
 Chemical reactions begin with reactants and end with
products.
Symbols used in Equations:
 Solid (s)
 Liquid (l)
 Gas (g)
 Aqueous solution (aq)
 Catalyst
H2SO4
 Escaping gas ( )
 Change of temperature ( )
5 types of Chemical Reactions:
 1. Synthesis: substances combine to form one
compound

A+X

2H2 + O2
AX
2H2O
  Practice predicting the products:
 a. sodium metal reacts with chlorine gas
 b. solid magnesium reacts with fluorine gas
5 types of Chemical Reactions:
 2. Decomposition: compounds break down into
smaller compounds and/or single elements

AX

2H2O
A+X
2H2 + O2
  Practice predicting the products:
 a. solid lead (IV) oxide decomposes:
 b. aluminum nitride decomposes:
5 types of Chemical Reactions:
 Decomposition exceptions:
 Carbonates and chlorates do not decompose into
single elements.
 Carbonates decompose to carbon dioxide and a
metal oxide.
CaCO3
CO2 + CaO
 Chlorates decompose to oxygen gas and a metal
chloride
2Al(ClO3)3
9O2 + 2AlCl3
5 types of Chemical Reactions:
 3. Single Replacement Reactions: when one element
replaces another in a compound; metal replaces metal;
nonmetal replaces nonmetal



A + BX
AX + B (metal replaces metal)
Y + BX
BY + X (nonmetal replaces nonmetal)
2Al + 3Pb(NO3)2
3Pb + 2Al(NO3)3
 Practice:
  a. Zinc metal reacts with aqueous hydrochloric acid
  b. Sodium chloride solid reacts with fluorine gas
5 types of Chemical Reactions:
 4. Double Replacement Reactions: two compounds
either trade metals or trade nonmetals









AX + BY
2KI + Pb(NO3)2
AY + BX
PbI2 + 2KNO3
Practice:
a. HCl(aq) + AgNO3(aq)
b. CaCl2(aq) +
Na3PO4(aq)
c. Pb(NO3)2(aq) +  BaCl2(aq)
d.  FeCl3(aq)
+   NaOH(aq)
e.  H2SO4(aq)   +  NaOH(aq)
f. KOH(aq)  + CuSO4(aq)
5 types of Chemical Reactions:
 5. Combustion Reactions: occurs when a
hydrocarbon reacts with oxygen gas; products are
always CO2 and H2O
 Practice:
  a.   C5H12 + O2
  b.
C10H22 + O2
Mixed Practice: ID the type of reaction
 a.  BaCl2 + H2SO4
BaSO4 + 2HCl
 b.  C6H12 +9 O2 
6CO2 + 6H2O
 c.  Zn + CuSO4
ZnSO4 + Cu
 d.  2Cs + Br2 
2CsBr
 e.  FeCO3 
FeO + CO2
Part 2: Balancing Equations
 Law of Conservation of Matter: matter cannot
be created or destroyed
 When a chemical reaction occurs, the amount of
Reactants must equal the amount of products. If an
equation does not have equal numbers of atoms on
each side, it is not balanced.
 To balance an equation, use coefficients which are
numbers in front of a symbol or formula. NEVER
change the subscripts!!
Part 2: Balancing Equations
 Al (s)
+
O2 (g)
Al2O3 (s)
 What is wrong with this equation?
 Fix it with coefficients!
 The final equation has 1 meanings:
 4 atoms of Al + 3 molecules of O2 yield 2 molecules
of Al2O3
Practice Balancing Equations:
 1.
H2(g) +
 2.
C3H8(g) +
 3.
B4H10(g) +
O2(g)
O2
O2(g)
H2O(l)
CO2(g)
+
H 2O
B2O3(g) + H2O(l)
Practice Balancing Equations:
 4. sodium phosphate + iron (III) oxide
sodium oxide + iron (III) phosphate
 5. sodium chloride + silver nitrate
sodium nitrate + silver chloride
 6. Iron (III) hydroxide
iron (III) oxide + water
Practice Balancing Equations:
 7. radium phosphide + sodium
sodium phosphide
+ radium
 8. cesium + sulfur
cesium sulfide
 9. potassium metal + chlorine gas
chloride
potassium
Practice Balancing Equations:
 Diatomic molecules are atoms that always
occur in pairs and should be written as pairs in
equations:
Part 4: Energy Involved in Chemical
Reactions:
 Endothermic Reactions: absorbs heat from the
environment, feels cold
 Exothermic Reactions: releases heat to the
environment, feels hot
Part 5: Activity Series:
 In single replacement reactions you have to use an activity series
to determine if an element can replace another:











 Li (More reactive)
 Mg
 Al
 Zn
 Cr
 Fe
 Pb
 H
 Cu
 Hg (Less reactive)
 Au
Part 5: Activity Series:
 Elements can replace other elements that are more
reactive (top can replace bottom)
 Example:
Pb2O3 + Cu
 These substance won’t react with each other. The
copper is not strong enough or “active” enough to
replace the lead.
Part 5: Activity Series:
 In addition to more active metals replacing less
active metals, nonmetals can also replace other
nonmetals (Most reactive at top…fluorine)
 Practice:
 a.  FeO2 + Cr
 b.  FeS + Hg
 c.  ZnCl2 + F2