1. Balancing Chemical Equations
Unit 6 Part B
Balancing Chemical Equations
ABClark-Grubb

2. H2 + O2 H2O Step #1 Write the formulas of the reaction
Hydrogen + Oxygen     Dihydrogen Monoxide    H2 + O2
H2O

3. Step #2
Count the number of atoms of each element on 
both sides of the reaction
Pull H2 + O2
H2O

4. THIS IS WRONG Never change the subscripts 

Would you want to drink a nice cold glass of 
hydrogen peroxide instead of water? H2 + O2
H2O2 =

5. Step #3
Change the coefficients to make the number of 
atoms equal on both sides
Must satisfy the law of conservation of mass, equal number of atoms on each side
__H2 +
__O2
__H2O

6. Tips for Balancing
Balance the types of atoms that 
appear in only one reactant and 
one product first.
Save H atoms and O atoms for last
If the same polyatomic ion appears on both sides of the equation, treat it as a single unit.

7. Example
AgNO3 +
CaCl2
AgCl +
Ca(NO3)2

8. More Examples Step #1 chlorine + sodium bromide
  bromine + sodium chloride
Step #1
Cl2 +
NaBr
Br2 +
NaCl

9. Step #2 & 3
__Cl2 +
__NaBr
__Br2 +
__NaCl

10. sodium + chlorine   sodium chlorideNa
Cl2 +
NaCl
It might help to make a table 
to keep track of what you 
need to balance.

11. Example + + AgNO3 Cu Cu(NO3)2 Ag
silver nitrate + copper  copper(II) nitrate + silver
AgNO3 + Cu
Cu(NO3)2 + Ag

12. Try these… Mg + N2  Mg3N2 P + O2  P4O10 CH4 + O2  CO2 + H2O
Na + H2O  H NaOH

13. Try these…
Mg N2  Mg3N2

14. Try these…
P O2  P4O10

15. Try these…
CH O2  CO H2O

16. Try these…
Na + H2O  H NaOH

17. Answers 3Mg + N2  Mg3N2 4P + 5O2  P4O10 CH4 + 2O2  CO2 + 2H2O
2Na + 2H2O  H2 + 2NaOH