Balancing Equations and
mols
Some Rules...
Remember...when elements are in a chemical reaction,
they form a new substance
Example: Sodium and Chlorine react to form Salt
(Sodium Chloride)
RULE ONE: In a compound name, The cation (positive
charge) is written before the anion (negative charge)
Example: NaCl because Na+ and Cl-
You Try
rule one
atoms vs molecules
RULE TWO:
when we have the smallest amount of an element that
can still maintain all of the element’s properties we call
that an ________________?
When we have the smallest amount of a compound that
can still maintain all of the compound’s properties we call
that a _____________?
You try
rule two
How many Atoms?
When we write atoms and molecules out there are often
numbers that come before and after in the formulas.
Rule 3: If the number comes after (is to the right) of an
element name and is subscript, it is the number of atoms
of that element (if no number there is one atom):
Ex: H2 has two atoms of H or H-H
Ex: H has one atom of H
Ex: H2O has two atoms of H and one atom of O
Number of molecules
If a compound is bracketed, the number that follows
refers to the number of molecules of that compound.
Ex: (SO4)6 has 6 molecules of SO4
This means there are 6 atoms of S and 6 x 4 atoms
of O (24 atoms of O).
Ex: H2(CO2)2 has 2 atoms of H and 2 molecules of
CO2
2 molecules of CO2 have 2 atoms of C and 2 x 2
atoms of O (4 atoms of O).
You Try
Rule Three
The numbers in Front
Rule 4: The numbers that come before the names of
elements and compounds in chemical equations refer to
the number of atoms or molecules that are written after
the number
These are the ONLY numbers that can be changed to
balance equations!!!!!
Ex: 4H2O means 4 molecules of H2O (8 H and 4 O
total)
Ex: 2H2SO4 + 4CO2 means 2 molecules of H2SO4
and 4 molecules of CO2
How many total H, S, O in 2H2SO4?
You try
Rule 4...
Balancing Equations
We write out chemical reactions in equations with the
reactants(what you start with) on the left side and
products(what you end up with) on the right side
Ex: Sodium and Chlorine react to form Sodium
Chloride
Na + Cl2
NaCl
PROBLEM: we started with two atoms of Cl but ended
with only one!
Balancing Equations
We must fix our problem by changing the numbers of
reactants and/or products to balance
WE CANNOT END UP WITH MORE OR LESS ATOMS
THEN WE STARTED WITH!
For Na + Cl2
NaCl we must add a 2 to the front of
Na and a 2 to the front of NaCl
2 Na + Cl
2 NaCl
Now it is balanced
Try with this way
H
H
O
O
H
ç√
H
O
H2 + O2
H
H2O H
H
H
O
H
H
O
ç√
H
O
2 H2 + O2 = 2H2O
H
H
O
You Practice
Balancing Equations