Download Chemical Reactions

Chapter 6
Counting Atoms
Subscripts indicate
the number of atoms
in a COMPOUND
Example
H2O
2 Hydrogen Atoms
1 Oxygen
The number 1 is
INVISIBLE
H2O
Coefficient
Subscript
H2O
Number of Number of
Molecules Atoms
2 Ag1Cl2
MULTIPLY
Coefficient x Subscript
Molecules:
Two
2 AgCl2
Atoms
2x1 = 2 Ag Atoms
2x2= 4 Cl Atoms
4 NaCl
Molecules = 4
Atoms:
4 Sodium Atoms
4 Chlorine Atoms
2 Ca(OH)2
Molecules = 2
Atoms:
2 Calcium Atoms
4 Oxygen Atoms
4 Hydrogen
3 H2O
Molecules = 3
Atoms:
6 Hydrogen Atoms
3 Oxygen Atoms
4 CO2
Molecules = 4
Atoms:
4 Carbon Atoms
8 Oxygen Atoms
An expression that
uses chemical
formulas and
symbols to describe a
reaction
Chemical Equation
R+R
P+P
R = Reactant

P= Product
Reactants
Start the reaction
At the Beginning
LEFT SIDE OF
ARROW
“ARROW”
Yields
Products
New substance(s)
Product = Finished
RIGHT OF THE
ARROW
Identify
Products and
Reactants
Reactants
Products
Na + Cl2
NaCl
Mg + O2
MgO
Al2O3
KCl + F2
Al + O2
KF + Cl2
To obey the Law of
Conservation of Mass
Atoms CANNOT be
created or destroyed
Mass of reactants =
Mass of products
Fe + S
14 g + 8 g
22 g
FeS
22 g
= 22 g
Mass of
Mass of
REACTANTS
PRODUCTS
Ca + Cl2
CaCl2
6 g + _?_ g
12 g
6 + ? g = 12 g
6g
Fe + S
? g + 16.0g
FeS
44.0 g
? + 16.0 g = 44.0 g
28.0 g
Ca + Cl2 CaCl2
1 Ca 2Cl 1Ca 2Cl
Balanced
Sn + Cl2
1Sn 2Cl
SnCl2
1Sn 2Cl
Balanced
Na + F2
NaF
1Na 2F
1Na 1F
Not Balanced
2Na + F2
2NaF
2X1=2
2X1 =2 (Na)
2X1 = 2 (F)
Balancing Chemical
Equations
Step 1: Write the
equation
Step 2: Count the
Atoms
Step 3: Use
COEFFICIENTS to
Balance Atoms
H2O
Coefficient
Subscript
Step 4: Double
Check Math
_Ag + _S
_Ag2S
_Mg + _O2
_MgO
_H2 + _N2
_NH3
2Ag + _S
_Ag2S
2Mg + _O2
2MgO
3H2 + _N2
2NH3
Classifying Chemical
Reactions
1. Synthesis
To put together
2 reactants
1 product
Example:
H2 + O 2
H2O
2. Decomposition
To tear apart
(breakdown)
1 reactant
2 products
Example
H2O
H 2 + O2
3. Single Replacement
2 reactants
2 products
Look for a SINGLE
element!
Example:
Cu2O + C Cu + CO2
Single
Element
Single
Element
4. Double Replacement
2 reactants
2 products
Compound + Compound
Compound + Compound
Example:
FeS +HCl
FeCl2 + H2S
H2O
Coefficient
Subscript
H2O
Number of Number of
Molecules Atoms
2 Ag1Cl2
MULTIPLY
Coefficient x Subscript
Molecules:
Two
2 AgCl2
Atoms
2x1 = 2 Ag Atoms
2x2= 4 Cl Atoms
4 NaCl
Molecules = 4
Atoms:
4 Sodium Atoms
4 Chlorine Atoms
3 H2O
Molecules = 3
Atoms:
6 Hydrogen Atoms
3 Oxygen Atoms
4 CO2
Molecules = 4
Atoms:
4 Carbon Atoms
8 Oxygen Atoms
Indicators
Compounds that
change color when it
contacts an acid or a
base
Properties of Acids
Sour taste
Reacts with metals
(corrosive)
Turns litmus paper red
Properties of Bases
Bitter Taste
Slippery Feel
Turns Litmus paper
Blue
Acids
Produce Hydrogen
+
Ions (H ) in water
Bases
Produce Hydroxide
ions (OH ) in water
The pH scale
The pH scale
Range of numbers
from 0-14
+
Indicates H ions
The pH scale
<7 ACID
 7 Water
>7 BASE