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BALANCING EQUATIONS &
CHEMICAL REACTIONS
Evidence of Chemical Change

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
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Changes in Energy (E)
Release of E as heat
Release of E as light
Production of sound
Reduction or increase of
temperature
Absorption or release of
electrical Energy

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Formation of new
substances
Formation of a gas
Formation of a
precipitate
Change in color
Change in odor
Conservation of Mass
Law of Conservation of Mass
 In any physical or chemical reaction, mass
is neither created nor destroyed; it is
conserved!
Reactants
Products
Same number of atoms on both
sides of the equation!
Balancing Equations
In every balanced equation
each side of the equation
has the same number of atoms
of each element
Important stuff!
Four abbreviations are
used to indicate
physical states of
chemicals: shown as
subscripts in the chemical
equation
(s) = solid
(l) = liquid
(g) = gas
(aq)= aqueous solution
(dissolved in water)
Symbols over the arrow
indicate the conditions of
the reaction
Heat
Pressure
Temperature
Catalyst
Reversible reaction
Balance this equation…
NaNO3 + CrCl3  NaCl + Cr(NO3)3
How would you “write” it?
Combination Reaction
or Synthesis Reaction
 Two or more simple substances react to
form a more complicated one
A + B  AB
Fe + S  FeS
Combination Reactions
We can predict the products of ionic compounds by
thinking about the charge!
Al (s) +
O2 (g) 
Cu (s) +
S(s)

Are there 2 possible products to this reactions
How would we “say” these equations?
Decomposition Reaction
 A decomposition reaction is the opposite
of a composition reaction - a complex
molecule breaks down to make simpler
ones.
AB  A + B
2 H2O  2 H2 + O2
Decomposition Reactions
Harder to predict the products…always remember
your diatomics.
Water is often a product!
HgO(s) 
NH4NO3
Decomposition Reactions
HgO(s)
2HgO(s)


2Hg(l)
+
O2 (g)
NH4NO3
NH4NO3


N2O
+
2H2O
The only way to really know is to do the
reaction!!
Single Replacement
 This is when one element trades places with
another element in a compound.
A + BC  AC + B
Mg + 2H2O  Mg(OH)2 + H2
Single Replacement Reactions
Easy to predict the products. Look at the ions…
remember that a cation has to bond to an anion!!
Don’t forget about diatomics!
Zn(s) +
H2SO4(aq) 
Na(s) +
H2O 
OOPS! Did we balance them?
Single Replacement Reactions

 ZnSO4(aq)
Zn(s) +
Zn(s) +
H2SO4(aq)
H2SO4(aq)
Na(s) +
Na(s) +
2Na(s)+
H2O 
H+OH-(l) 
2H+OH-(l)  2NaOH
+ H2(g)
+ H2(g)
Single Replacement Reactions
Reactivity of a metal makes a difference!
If a metal is more reactive than the metal it is
displacing a rxn will occur. If the metal is
less reactive than the metal it is
displacing, a rxn will not occur.
Metal Reactivity
Increases down a group
Decreases across a period
Brainiacs-- Metal Reactivity
Reactivity in Single Displacement
+ KMnO4  CsMnO4
Will this occur??
Cs
Na
+
KMnO4  NaMnO4 + K
Will this occur?
Double Replacement Reaction
 This is when the anions and cations of two
different molecules switch places, forming
two entirely different compounds
AB + CD  AD + CB
Pb(NO3)2 + 2KI  PbI2 + 2KNO3
Double Replacement Reactions
Generally take place between two ionic compounds in
aqueous solution
Pb(NO3)2 + 2KI  PbI2 + 2KNO3
Double Replacement Reactions
2NaCl + H2SO4 
Double Replacement Reactions
Ca(OH)2(aq) + 2HCl(aq) )
Combustion Reactions
 A combustion reaction is when oxygen
combines with another compound or
element producing energy.
 When hydrocarbons (C?H?) combust,
water, carbon dioxide and energy are
produced.
C10H8 + 12 O2  10 CO2 + 4 H2O + Energy
Combustion of Naphthalene
Combustion Reactions
Combustion of propane:
C3H8 +
O2

Combustion of methane:
CH4 +
O2

Combustion of butene (this one is tricky!)
C4H6 +
O2

Teacher Demo Extraordinaire!
What is a flame video- Science Friday
http://www.sciencefriday.com/video/06/08/2012/
what-is-a-flame.html
Recap: 5 Types of Reactions
1.
2.
3.
4.
5.
Combination
Decomposition
Single Replacement
Double Replacement
Combustion
Warm Up: Predict the products, balance
and classify the following reactions.
Li + MgCl2 
C6H12 + O2 
Ca(NO3)2 + NaOH 
Types of Rxns Lab
Take about 10 minutes to do the prelab
questions on the lab. Most of the answers
should be in your CB notes.
Warm UpBalance the following combustion equations:
C4H4 +
O2 
CO2 + H2O
C3H6 +
O2 
CO2 + H2O
C7H14 +
O2 
CO2 + H2O
Types of Reaction Lab
a. Synthesis: Mg + O2
b. Decomposition CuCO3
c. Single Replacement Zn + HCl
d. Double Replacement PbNO3 + KI
Finish the lab
You have 20 minutes to get it done!
Be sure that all your questions are answered!
Debrief Types of Rxns Lab
Types of Reaction Lab
Synthesis: Mg + O2 
Did the mass of the system change after the reaction
took place?
Did you detect the presence of ammonia gas?
Endothermic or exothermic?
Types of Reaction Lab
Decomposition CaCO3 
What evidence indicates a chemical reaction.
How do you know that carbon dioxide was formed?
Endothermic or exothermic?
Types of Reaction Lab
Single Replacement
Zn + HCl 
What evidence did you see?
What was in the little tube– how do you know?
Endothermic or exothermic?
Types of Reaction Lab
Double Replacement
PbNO3 + KI 
What evidence did you see?
Endothermic or exothermic?
Work on classifying the types of
reactions on your balancing WS.
When you finish, you can start working on the
back side of the Current Mole WS…. The front
side should be complete!
Warm Up
Balance and classify the following reactions:
1. Zn
+
H2SO4
2. CaCl2
+
3. C3H8
+
→
NaNO3 →
O2 →
H2
+ Zn(SO4)2
Ca(NO3)2
CO2
+
+
H2O
NaCl
You should have most of these WS
done!
1. Balancing equations WS– classified rxn type
2. Mole Practice WS…
Finish both of these… turn them in!
Work on the Review!
Due the beginning of class on Monday!
Test after we go over the review!!
Warm Up
Balance and classify the following reactions:
→
1. Na
+
H2CO3
2. NaF
+
Ca(NO3)2 →
3. C5H12
+
O2 →
H2
+ Na2CO3
NaNO3
CO2
+
+
H2O
CaF2
Warm Up- part 2
Determine the molar mass of MgF2
Convert 5.7 g of magnesium fluoride to moles.
Convert 6.3 g of magnesium fluoride to
molecules.
Warm Up Quiz
1. Determine the molar mass of Na3PO4
2. How many moles in 10.6g of Na3PO4
3. How many atoms in 0.50 mol Al?
4. How many atoms in 3.6 g of carbon?
Warm Up
Balance and classify the following reactions:
1. K
3. CH12
+
H3PO4
+
O2 →
→
H2
CO2
+ K3PO4
+
H2O