 Indicators of a chemical reaction•
Color change
• Producing a gas
• Heat/light energy released
• Formation of a precipitate
 Chemical equation - Describes a chemical change.
 Parts of a chemical equation:
Reactant
Product
Zn + 2HCl
ZnCl2 + H2
Coefficient
Reaction symbol
 Reactant - The substance(s) that exist before a
reaction begins
 Written on left side of equation.
 Product - The new substance(s) formed by the
reaction.
 Right side of equation.
 Subscript – indicates the number of atoms of an element
in a compound.
 EX: H2O
 2 atoms of hydrogen (H)
 1 atom of oxygen (O)
 Coefficient – indicates how many units of each compound
is in a chemical reaction.
 EX: 3 H2O
 3 molecules of H2O
 2H2 + O2  2H2O
 Lavoisier: Matter is neither created nor destroyed
in a chemical reaction.
 In other words, the number and type of atoms going
INTO a reaction must be the same as the number and
type of atoms coming OUT.
 A Balanced Chemical Equation must obey the Law of
Conservation of Mass.
 CH4 + O2  CO2 + H2O
Reactant Side
1 carbon atom
4 hydrogen atoms
2 oxygen atoms
Product Side
1 carbon atom
2 hydrogen atoms
3 oxygen atoms
A Balanced Equation

CH4 + 2O2  CO2 + 2H2O
Reactant Side
1 carbon atom
4 hydrogen atoms
4 oxygen atoms
Product Side
1 carbon atom
4 hydrogen atoms
4 oxygen atoms
1. Matter cannot be created or destroyed.
2. Subscripts cannot be added, removed, or changed.
3. You can only change coefficients.
•
4. Coefficients can only go in front of chemical compound
• NEVER in the middle of a formula.
A few extra tips:
Try balancing big formulas first; save single elements for last.
If the same polyatomic ion appears on both sides of the
equation, it’s usually okay to treat it as one unit.
There is no one particular way to balance equations. Some
equations are harder to balance than others and might require
some creativity to solve.
 Balance the following equation by adjusting
coefficients.
N2 + 3 H2  2NH3
reactants products
N
2
21
H
6
2
63
 Balance the following equation by adjusting
coefficients.
2 KClO3  2 KCl + 3 O2
reactants products
K
1
2
12
Cl
1
2
1
2
O
3
6
2
6
 Balance the following equation:
2 C2H6 + 7 O2 4 CO2 + 6H2O
 Balance the following equation:

4 Fe +3 O2  2 Fe2O3
My Mole-called Life
AKA Mole-sterpiece Theatre
Chemical Reaction Types
• synthesis – reaction where 2 or more substances combine to
form one
• A + B → AB
• Ex: 2H2 + O2 → 2H2O
• decomposition – reaction where a compound
decomposes(breaks apart) into multiple substances
• AB → A + B
• Ex: 2KClO3 → 2KCl + 3O2
• single replacement - single element replaces another
element in a compound
• A + BC → AC + B
• Ex: 2Ag + FeCl2 → Fe + 2AgCl
My Mole-called Life
Chemical Reaction Types Continued…
• Double replacement - two elements in different
compounds switch places
• AB + CD → AD + BC
• Ex: NaOH + HCl → NaCl + HOH(H2O)
• Combustion Reaction - Hydrocarbon combines with
oxygen to form water and carbon dioxide
• hydrocarbon – any compound made from carbon and
hydrogen
• hydrocarbon + O2 → CO2 + H2O
• Ex: C2H4 + 3O2 → 2CO2 + 2H2O