Download Chapter 6 Unit Notes Chemical Reactions I can describe the


Chemical Reaction – Occurs when
substances undergo chemical
changes to form new substances
› Usually you can see a chemical change
take place!

Signs a chemical reaction is happening:
› 1. Formation of a separate gas (bubbles or
fizz)
› 2. Formation of a separate solid
› 3. See light or feel heat
› 4. Color change (like burning)
A physical change keeps the same
substance, it just looks different.
 A chemical change forms a new
substance.
 In a chemical reaction there are 2 parts
that must be the same on both sides!

In the picture to the right,
there are the same
amounts of Carbon,
Hydrogen, and Oxygen
on both sides!
Total energy before the reaction
is equal to the total energy of the
products at the end.
 There are two types of reactions in a
reaction:

› 1. endothermic (heat enters)
› 2. exothermic (heat exits)

Exothermic Reaction – The
temperature of the surroundings
rise because energy is released
› Examples:
 1. Combustion
 2. Fire
 3. Hand warmers

Endothermic Reaction – A chemical
reaction that needs more heat
› Examples:
 1. Plastics becoming brittle after being left in
the sun
 2. Photosynthesis
 3. Ice cube melting

Chemical Equations – A
representative of a chemical
reaction that uses symbols and
formulas to show reactants and products
› Reactants = left side
› Products = right side
Use coefficients to represent the
number of units of each substance
in a reaction (kind of like the
number of ingredients in a recipe)
 Use subscripts to represent the number
of atoms in a molecule of a particular
element

Choosing coefficients becomes
easier with practice
 At first it is trial and error
 A four-step process:

› 1. Describe the reaction in words in your
head
› 2. Write the equation using formulas and
symbols if it is not already written that way
› 3. Check for balance with numbers under
› 4. Add coefficients where needed for
balance
P
+ O2  P4O10 (Find how many total atoms)
1
P
4
2
O
10
 Now use coefficients to balance
 4P + 5O2  P4O10
4
P
4
10
O
10
 Al2O3

 Al + O2
Answer:
› 2Al2O3  4Al + 3O2
 BaCl2
+ H2SO4  BaSO4 + HCl
 Answer:
› BaCl2 + H2SO4  BaSO4 + 2HCl

Factors that cause chemical
reactions to happen faster:
› High temperatures (think about mold)
› Large surface area because there are more
particles that can react
› Concentration level
› High pressure
› Catalysts