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Balancing Chemical Equations
BALANCING EQUATIONS
Law of Conservation of Mass applies to
chemical reactions.
 Discovered by Antoine Lavosier.
 “Matter is neither created nor
destroyed in a chemical reaction”.

An Unbalanced Equation
H2 + O2


H2O
Why is this equation unbalanced?
Answer: There are 2 atoms of O in the
reactant, but only 1 in the product.
How to Balance
An equation is balanced by adding
coefficients.
 Trial & error procedure.
 Goal: equal numbers of atoms of
each element appear on both sides
of the arrow.

REMEMBER:

The coefficient (number in front of a
chemical formula) multiplied by the
subscript gives the total number of
atoms.
EXAMPLE
2 H2 means there are 2 x 2
atoms of hydrogen for a total of
4 hydrogen atoms.
 2H2O means there are 4 atoms
of hydrogen and 2 (2 x 1)
atoms of oxygen.

SO LETS BALANCE



H2 + O2
H2O
The H’s are balanced but the O’s are
not.
Put a “2” in front of the H2O.
NOW IT LOOKS LIKE THIS




H2 + O2
2H2O
But now there is a new problem!
There are now 4 H on the right!
Let’s fix it!!!
HERE’S HOW

H2 + O2
2H2O

Put a 2 in front of the H2

2H2 + O2
2H2O
IS IT BALANCED?
2H2 + O2
2H2O



REACTANT ATOMS
4H
2O



PRODUCT ATOMS
4H
2O
•CONGRATULATIONS, IT’S
BALANCED!!!
WARNING!


NEVER CHANGE A SUBSCRIPT!
(Because that changes the formula of the
compound!)
NEVER PUT COEFFICIENTS IN
THE MIDDLE OF A FORMULA!
TRY THIS ONE

__ H2 + __ Cl2

H2 + Cl2


__ HCl
2HCl
What type of chemical reaction is this?
Answer: composition or synthesis
TRY THIS ONE:

__Zn + __HCl

Zn + 2HCl


__ZnCl2 + __H2
ZnCl2 + H2
What type of chemical reaction is this?
Answer: single replacement
TRY THIS ONE:

__KClO3

2KClO3


__KCl
2KCl
+ __O2
+
3O2
What type of chemical reaction is this?
Answer: decomposition
TRY THIS ONE:




_H2SO4 + _Al(NO3)3
3H2SO4 + 2Al(NO3)3
_HNO3 + _Al2(SO4)3
6HNO3 + Al2(SO4)3
What type of chemical reaction is this?
Answer: double replacement
Chapter 8 SUTW Prompt




Describe the method for balancing a chemical
equation using proper coefficients.
1 RDF + 3 examples (Hint: steps) in pink.
Complete a 6 -8 sentence paragraph using
the SUTW paragraph format. Highlight using
green, yellow, and pink.
Due Date: Tomorrow (start of class).