The document discusses how to balance chemical equations by ensuring the total number of atoms on both sides of the equation are equal. It explains that coefficients are used to represent the number of molecules in a reaction, while subscripts indicate the number of atoms in a molecule. The steps to balance an equation are to: 1) Write the unbalanced equation, 2) Count the atoms on each side, 3) Use coefficients to make the atoms equal on both sides. Examples are provided to demonstrate balancing equations through adjusting coefficients and verifying the balanced atoms.

1. Balancing Equations
Just repeat:
“I know I can, I know I can!”

2. Balancing equations
 Conservation


of Matter: During a chemical
reaction, atoms cannot be created or
destroyed!
Due to the conservation of matter, equations
MUST be balanced!
Thus, the total number of atoms in the
products must equal the total number of
atoms in the reactants
REMEMBER: The atoms are only being
rearranged during the reaction!

3. Coefficients vs. Subscripts
 Subscripts
tell us how many atoms
there are in the molecule.
H2O This tells us that there are 2
Hydrogen
atoms bonded to one
Oxygen atom
 Coefficients
tell us how many
molecules there are.
2 H2O This tells us that there are 2
molecules of H2O

4. Coefficient
2H2O
Subscript

5. Use of coefficients in balancing
 When
balancing a chemical equation,
we can ONLY add coefficients!
 Coefficients
do not change the molecules
in the reaction, they merely tell us how
many molecules were needed for the
reaction to occur.
 We cannot add/change subscripts when
balancing the equation.
Any
guesses why???

6. Don’t use subscripts!!!!
 Because…..
 It
changes the actual molecule!!! Which
would change either the reactant or the
product!
Example:
H2O is water, but H2O2 is hydrogen
peroxide. That is a huge difference!
Ok, let’s try balancing some equations together!

7. How to balance an equation
 FIRST
STEP: Write out the equation
with the reactants and products in the
formula:
MgO + HBr ---> MgBr2 + H2O
(Magnesium oxide and Hydrogen Bromide
becomes Magnesium Bromide and Water.)

8. How to balance an equation
 SECOND
STEP: Count the Atoms of
each element on both sides of the
equation.
MgO + HBr ---> MgBr2 + H2O
1 Mg
1O
1H
1 Br
1 Mg
1O
2H
2 Br

9. How to balance an equation
 THIRD
STEP: Use coefficients to
balance the equation
MgO + HBr ---> MgBr2 + H2O
We need a total of two hydrogen and
bromine on the reactants side in order
to balance this equation.

10. How to balance an equation
 And
we’re done! Our balanced
equation:
MgO + 2HBr ---> MgBr2 + H2O
Double check your work, by counting again:
1 Mg
1 Mg
1O
1O
2H
2H
2 Br
2 Br

11. Try one on your own!
H
+ O  H 2O
H- 1
O- 1
H- 2
O- 1
2H + O  H2O

12. Let’s do another, for fun!!
Fe + HCl ---> FeCl2 +H2
1 Fe
1H
1 Cl
1 Fe
2H
2 Cl
Fe + 2HCl ---> FeCl2 +H2

13. Let’s try a couple more…
N2 + O2 ---> N2O5
2N
2O
2N
5O
We need to balance out the Oxygen first,
then the Nitrogen. This gives us…
2N2 + 5O2 ---> 2N2O5
4N
10 O
4N
10 O

14. One More…
C2H4 + O2 ---> CO2 + H2O
2C
4H
1C
2H
2O
3O
C2H4 + 3O2 ---> 2CO2 + 2H2O