1. CHEMICAL EQUATIONS
BY MS. PACHECO

2. RECALL… The law of conservation of matter:
Matter can neither be created nor destroyed in a chemical reaction.

3. Therefore…
The number of atoms of each element must remain the same before and after a chemical reaction.
To do this, you BALANCE the equation.

4. To balance an equation…
You may use COEFFICIENTS only
(Numbers written before a formula)

5. For example…
Ca + O2  CaO
left side right side
Ca= Ca =1
O= O=1

6. To balance the equation…
Ca + O2  CaO
You need to increase the number of oxygens on the right.
Remember that you can only use COEFFICIENTS!!

7. Ca + O2  CaO Ca + O2  2CaO Add a 2 in front of the CaO on the right.
Left side Right side
Ca= Ca=2
O= O=2
The O’s balance, but now the Ca’s are off!!

8. Ca + O2  2CaO
Now, add a 2 in front of the Ca on the left.
2Ca + O2  2CaO
Left side right side
Ca= Ca=2
O= O=2
The equation is balanced and the law of conservation of matter is satisfied!!!!

9. Now your turn… Balance the following equation.
Remember to use coefficients only!!!
Al + F2  AlF3

10. Al + 3F2  2AlF3 Then, balance the Al’s 2Al + 3F2  2AlF3
HINT: Odd-even rule
Al + 3F2  2AlF3
Then, balance the Al’s
2Al + 3F2  2AlF3

11. Also…
Complete chemical equations use letters after the formulas to represent the state of the compound.
(s) for solid
(l) for liquid
(g) for gas

12. Example… Na + Cl2NaCl Na is a solid Cl2 is gas NaCl is a solid So…
Na(s) Cl2(g)NaCl(s)

13. Lastly…
Diatomic elements: When the following elements are BY THEMSELVES (not part of a compound), they combine as a pair of atoms.
H2, N2, O2, F2, Cl2, Br2, I2

14. Example…
Nitrogen gas combines with hydrogen gas to produce gaseous ammonia (NH3)
N H2  NH3
Don’t forget to balance!!!
Include the physical state of each!!!

15. N2 + H2  NH3 Left side right side N=2 N=1 H=2 H=3
Use odd-even rule on H’s
N H2  2 NH3
N= N=2
H= H=6

16. Include the physical state of each!!!
N H2  2 NH3
N2(g) H2(g) 2 NH3(g)