Chemical Reactions
Chemical Reaction…
Not a Chemical Reaction…
What is a Chemical Reaction?
• A process in which new substances with new
chemical and/or physical properties are
formed.
• A burning piece of paper (Chemical Reaction):
paper  ashes, water vapor, and carbon dioxide
• Dissolving salt in water (No Reaction):
Salt
+
Water →
Salt
+ Water
Parts of a Chemical Equation
Na+ Cl → NaCl
sodium and chlorine yields sodium chloride
Reactants
The substances that
you start with. In this
case:
Sodium and Chlorine
“Yields”
This arrow tells
you that the
reactants
become the
products
through a
chemical
reaction.
Products
The substances
you end with.
In this case:
Sodium
Chloride
Chemical Equations
Mg + O2 → MgO
magnesium and oxygen yields
magnesium oxide
H2O → H2 + O2
water
yields hydrogen and oxygen
C4H10 + O2→CO2 + H2O
butane
and oxygen yields carbon dioxide and water
Types of Chemical Reactions
Type 1: Synthesis
• In a synthesis reaction, two (or more) simple
substances form a more complex substance.
• Synthesis: Two Become One
• A + B → AB
Synthesis Example
Na + Cl → NaCl
sodium and chlorine yields sodium chloride
Types of Chemical Reactions
Type 2: Decomposition
• In a decomposition reaction, a complex
substance is broken down into two (or more)
simpler substances.
• Decomposition: One Becomes Two
• AB → A + B
Decomposition Example
H2O2 → H2O + O2
hydrogen peroxide yields water and oxygen
Types of Chemical Reactions
Type 3: Single Replacement Reaction
• In a single replacement reaction, a single
element replaces another element in a
compound.
• Single Replacement: Start with one
compound, end with a different compound.
A +
BC
B +
AC
Single Replacement Reaction
Single Replacement Example
Zn + HCl → H2 + ZnCl2
zinc and hydrochloric acid yields hydrogen and zinc chloride
Types of Chemical Reactions
Type 4: Double Replacement Reaction
• In a double replacement reaction, elements
from two compounds switch places and form
two new compounds.
• Double Replacement: Start with two
compounds, end with two different
compounds.
AB
+ CD
CB + AD
Double Replacement Reaction