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Chemical Reactions
 A chemical reaction is also known as a chemical ______________________________.
 A chemical reaction is when one or more ____________________________ are
changed. Bonds are _______________________________ and rearranged to reform
new substances.
Reactants
Products

_________________________
_________________________
 There are 6 indicators (observations) of a chemical reaction :
_______________________________________
_______________________________________
_______________________________________
_______________________________________
_______________________________________
_______________________________________
 In a chemical reaction, the law of _____________________________________ of mass is
important. This law states that __________________________ can neither be created
nor destroyed, just changed in form.
 A ___________________________________________ describes a chemical reaction using
symbols and formulas.
Fe(s)
+
O2(g)
 Symbols you should know:
(s) _________________________
(g) _________________________


_________________________
_________________________
Fe2O3(s)

(l)
unbalanced
_____________________________
(aq) _____________________________
+
_____________________________
X

______________________________

______________________________
On the product side ONLY
 __________________________
 A chemical reaction must have 2attributes:
1. It must contain correct chemical formulas
o BrINClHOF is the mnemonic for all of the 7 diatomic molecules. They
get a subscript of 2 when by themselves.
o Always check the charges of an ionic compound when translating an
equation or predicting a product.
2. It must be balanced!
o _the number of atoms of each element on the reactant side must
__________________________ the number of atoms of each element on the
product side.
o ______________________________________are small whole numbers placed in
front of a chemical formula in order to balance the atoms
o A “1” is understood
o The coefficient multiplies by every subscript within a chemical
formula
Examples:
CaCl2
3 CaCl2
3 Ca3(PO4)2
Translating a word equation into a skeletal equation
1. Hydrogen gas reacts with liquid bromine to form hydrogen bromide gas.
2. Carbon monoxide reacts with oxygen gas to form carbon dioxide.
3. Calcium carbonate decomposes to form calcium oxide and oxygen gas
Tips for Balancing Equations:
1. Balance each atom one at a time leaving HYDROGEN and OXYGEN for last
2. Balance polyatomic ions that are found on both sides as chunks, instead of
single atoms
3. If there is an odd number of an element on one side and an even number on
the other side, use a coefficient of 2 to even out the odd number.
4. Combustion reactions are more easily balanced if you start off by balancing
the carbon and then hydrogen in the hydrocarbon. Then balance the oxygen
last.
5. Once you think the equation is balanced, always recheck and count all atoms
over again to make sure they are equal on both sides.
6. If the coefficients can be simplified, do so!
Balancing Practice:
1.
___ H2
+ ___ Cl2  __ HCl
2.
___ KClO3  ___ KCl + ___O2
3. ___ NH4NO3 + ____ Ca3(PO4) 2  ____ (NH4)3PO4 + ___ Ca(NO3) 2
4. ____ C6H14 + ___ O2  ___ CO2 + ___ H2O
5. _____ Z n + _____ HCl  ____ ZnCl2 + ___ H2
5 Types of Reactions
1. Combination (Synthesis): when 2 or more _______________________________
combine to form one single _____________________________.
A
+
B
AB

2 or more elements
OR
2 or more compounds
1 single product
Examples:
Fe +
S
FeS
CaO +
H2O 
Ca(OH) 2
2. Decomposition: when 1 _______________________________ breaks down or decomposes
to form 2 or more _____________________________________. These require
_____________________ to get started such as heat, light, or electricity.
AB
A

1 single reactant
Hg +
NaHCO3 
O2
Na2CO3 +
H2O +
B
2 or more elements
OR
2 or more compounds
Examples:
HgO 
+
CO2
3. Single Replacement: when a more reactive element __________________________ a
less reactive element. Must use the _______________________________ chart, which
predicts if the reaction will take place. Look at your reference sheet for the
chart.
 Elements on the top of the chart are _____________________ reactive than the
elements on the bottom. Elements can replace other elements below
them on the chart. For example: Lithium can replace Aluminum
A + BC
AC

element & aqueous compound
+
B
element & aqueous compound
Examples:
Cu + AgNO3 
Cl2
+
KBr
CuNO3 +
Ag
KCl + Br2

4. Double Replacement: when the positive ions of each aqueous compound replace
each other.
AB + CD
AD

2 aqueous compounds
+
CB
2 aqueous compounds
Examples:
KI + Pb(NO3) 2 
AgNO3
+
KNO3 +
CuCl2 
PbI2
AgCl + Cu(NO3)2
5. Combustion: the burning of a substance by reacting it with oxygen (O2)
Hydrocarbon + O2

Fe
Fe2O3
+
O2

Examples:
CH4 + O2 
C4H10 + O2 
CO2 +
CO2 +
H2O
H2O
CO2 +
H2O