1. Ch. 11.2 Notes Balancing Chemical Equations

2. Key Vocabulary
Coefficients: numbers in front of a formula used to balance chemical equations (BIG numbers)
Example: 3 H2O
- Here we have 3 mols of H2O

3. Subscripts: The small numbers in the bottom right of a formula
Subscripts: The small numbers in the bottom right of a formula. Indicates how many of that atom in the compound. We DO NOT change these.
Example: MgF2
- This molecule contains 1 Mg atom and 2 F atoms.

4. Skeleton Equation: Unbalanced chemical equation.
- Now let’s try balancing!

5. Write a skeleton equation, this is NOT balanced
Mg + O2  MgO
STEP ONE: list the atoms that are involved on each side of the arrow
Mg + O2  MgO Mg O

6. Mg + O2  MgO Mg + O2  MgO 2 STEP TWO: start balancing
Just count up the atoms on each side
Mg + O2  MgO Mg O 1 1 2 1
STEP THREE: The numbers aren’t balanced so add coefficients to balance
Mg + O2  MgO Mg O 1 2 2 2 2
And adjust totals

7. This follows the Law of Conservation of Mass
But the numbers still aren’t equal, so add another coefficient 2
Mg + O2  MgO Mg O 1 2 2
And adjust totals again
NOW BOTH SIDES HAVE EQUAL NUMBERS OF ATOMS
This follows the Law of Conservation of Mass

8. Try to balance these equations using the same method:
[1] Na + Cl2  NaCl
[2] CH4 + O2  CO2 + H2O
[3] Li + HNO3  LiNO3 + H2
[4] Al + O2  Al2O3

9. How did you get on??
Here are the answers:
[1] 2 Na + Cl2  2 NaCl
[2] CH O2  CO H2O
[3] 2 Li + 2 HNO3  2 LiNO3 + H2
[4] 4 Al + 3 O2  2 Al2O3
***When you’re done, pair up with somebody at your table and grab a laptop.