1. Chemical Reactions
Chapter 10

2. Chemical Equations N2 + 3H2 -> 2NH3 N2 + H2 -> NH3
coefficients tell the number of molecules in a reaction
N2 + H2 -> NH3
subscripts tell the number of atoms in a molecule

3. Chemical Equations N2 + 3H2 -> 2NH3 N2 + 3H2 -> 2NH3
The products are on the:
RIGHT SIDE
N2 + 3H2 -> 2NH3
The reactants are on the:
LEFT SIDE

4. Chemical Equations N2 + 3H2 -> 2NH3 N H
Law of Conservation of Mass: Mass can not be created or destroyed.
Therefore: the number of atoms of each element must be the same on both sides of the equation.
How many Nitrogens does each side have?
How many Hydrogens does each side have? 2 2 6 6

5. Balancing Chemical Equations
How do we balance a chemical equation?
We use the scoreboard method
N2 + 3H2 -> 2NH3 N H
Our goal is to have both sides be even.
In other words, our goal is to TIE! 2 2
scoreboard 6 6

6. Chemical Equations H2 + O2  H2O H O Is it balanced?
We need to add coefficients to make it balanced
Is it balanced now? 2 2 4 2 2 4 2 1 2

7. Chemical Equations
Fe O2  Fe2O3 Fe O 4 3 2 4 1 2 4 6 2 3 6

8. Chemical Equations FeCl3 + KOH  KCl + Fe(OH)3 Fe Cl K OH
Here, OH is a polyatomic ion, so we leave it as OH on our scoreboard 3 3 1 1 3 1 3 3 3 1 1 3 1 3

9. Chemical Equations C3H6 + O2  CO2 + H2O C H O 2 9 3 6 6 3 6 3 1 3 6
in some reactions, where the O is split between two compounds, save it for last, and write it as two separate numbers
We now have an odd number of oxygens.
Double the organic molecule and rebalance. 2 9 3 6 6 3 6 3 1 3 6 12 6 2 6 12 18 2
2 + 1 6 3 12 6

10. Now you practice.
Pick a partner and work on your Balancing Practice Worksheet.
Be sure to show your scoreboards!