1. Balancing Chemical Equations
Homework 3-1
Balancing Chemical Equations
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2. Example: Level 1 Balancing Problem
K Br2 → KBr
Atomic Level Picture: K = Br =
Atom Count:
K: Br: → K: Br: 1 2 1 1

3. Example: Level 1 Balancing Problem
K Br2 → 2 KBr
Atomic Level Picture: K = Br =
Atom Count:
K: Br: → K: Br: 1 2 2 2

4. Example: Level 1 Balancing Problem
2 K Br2 → 2 KBr
Atomic Level Picture: K = Br =
Atom Count:
K: Br: → K: Br: 2 2 2 2

5. Level 1 Practice: Balance the following reactions:2 2
1) Mg + O2 → MgO
2) Na3N → Na + N2
3) Al MgO → Mg + Al2O3 2 6 2 3 3

6. Level 2: Helpful hint: Least Common Multiple:
Example: KClO3 → KCl O2
K: Cl: O: → K: Cl: O:
Problem: 2 O on right will not divide evenly into 3 O on left. What is the least common multiple of 2 and 3? 1 1 3 1 1 2 6

7. Level 2: Helpful hint: Least Common Multiple:
Example: KClO3 → KCl O2
K: Cl: O: → K: Cl: O:
Problem: 2 O on right will not divide evenly into 3 O on left. What is the least common multiple of 2 and 3? 2 1 1 3 1 1 2 6

8. Level 2: Helpful hint: Least Common Multiple:
Example: KClO3 → KCl O2
K: Cl: O: → K: Cl: O:
Problem: 2 O on right will not divide evenly into 3 O on left. What is the least common multiple of 2 and 3? 2 2 1 3 1 1 2 6

9. Level 2: Helpful hint: Least Common Multiple:
Example: KClO3 → KCl O2
K: Cl: O: → K: Cl: O:
Problem: 2 O on right will not divide evenly into 3 O on left. What is the least common multiple of 2 and 3? 2 2 2 3 1 1 2 6

10. Level 2: Helpful hint: Least Common Multiple:
Example: KClO3 → KCl O2
K: Cl: O: → K: Cl: O:
Problem: 2 O on right will not divide evenly into 3 O on left. What is the least common multiple of 2 and 3? 2 2 2 6 1 1 2 6

11. Level 2: Helpful hint: Least Common Multiple:
Example: KClO3 → KCl O2
K: Cl: O: → K: Cl: O:
Problem: 2 O on right will not divide evenly into 3 O on left. What is the least common multiple of 2 and 3? 2 3 2 2 6 1 1 2 6

12. Level 2: Helpful hint: Least Common Multiple:
Example: KClO3 → KCl O2
K: Cl: O: → K: Cl: O:
Problem: 2 O on right will not divide evenly into 3 O on left. What is the least common multiple of 2 and 3? 2 3 2 2 6 1 1 6 6

13. Level 2: Helpful hint: Least Common Multiple:
Example: KClO3 → KCl O2
K: Cl: O: → K: Cl: O:
Problem: 2 O on right will not divide evenly into 3 O on left. What is the least common multiple of 2 and 3? 2 2 3 2 2 6 1 1 6 6

14. Level 2: Helpful hint: Least Common Multiple:
Example: KClO3 → KCl O2
K: Cl: O: → K: Cl: O:
Problem: 2 O on right will not divide evenly into 3 O on left. What is the least common multiple of 2 and 3? 2 2 3 2 2 6 2 1 6 6

15. Level 2: Helpful hint: Least Common Multiple:
Example: KClO3 → KCl O2
K: Cl: O: → K: Cl: O:
Problem: 2 O on right will not divide evenly into 3 O on left. What is the least common multiple of 2 and 3? 2 2 3 2 2 6 2 2 6 6

16. Level 2: Practice 4) Al + O2 → Al2O3 5) Al + HCl → AlCl 3 + H2 4 3 2 3
5) Al HCl → AlCl H2 4 3 2 3 3

17. Level 2: Practice 4) Al + O2 → Al2O3 5) Al + HCl → AlCl 3 + H2 4 3 2 2
5) Al HCl → AlCl H2 4 3 2 2 6 2 3

18. Level: Complex problems
Level 3: Most complex problems have elements that appear in multiple terms on each side and/or issues with odd / even.
Hints: Balance elements that appear in only 1 term on each side first.
Remember that if the subscript for an element term on one side is an even # and is odd in one term on the other side, doubling odd #’s is the easiest way to convert odd #’s to even #’s.

19. Example #1: C H O CH4 + O2 → CO2 + H2O
Start with or because those elements appear in only 1 term on both sides.
Save for last because it appears in multiple terms and would require filling in 3 coefficients simultaneously which is more complex. C H O

20. Example #1: C H O CH4 + O2 → CO2 + 2 H2O
Start with or because those elements appear in only 1 term on both sides.
Save for last because it appears in multiple terms and would require filling in 3 coefficients simultaneously which is more complex. C H O

21. Example #1: C H O CH4 + 2 O2 → CO2 + 2 H2O
Start with or because those elements appear in only 1 term on both sides.
Save for last because it appears in multiple terms and would require filling in 3 coefficients simultaneously which is more complex. C H O

22. Practice C: H: O: C: H: O: 6) C6H12O6 → C2H6O + CO2 2 2 4 +1 2 2 +2 4
2+1 6
1+2 3 3 6 5 12 6 4

23. 7) C5H12 + O2 → CO2 + H2O C: H: O: C: H: O: 8 5 6 10+1 6 5 12 2 1 2
2+1 16 5 12 16 11

24. 3 8) C2H5OH + O2 → CO2 + H2O 2 3 C: H: O: C: H: O: 3 4 +1 2 6 1+2 1 2
2 +1 3 2 6 5 3 7

25. Odd-even: H2O2 → H2O + O2 2 2 Example #1: H: 2 O: 2 H: 2 O: 1 + 2 2 4

26. Odd/Even Example #2: C4H10 + O2 → CO2 + H2O 10 8 2 13 4 5
C: H: O: C: H: O: 10 8 2 13 4 5 10 16 4 8 5 10 4 10 2 1 2
2 + 1 13 8 20 26 8 20 26

27. 9) C8H O2 → CO H2O
10) NH NO → N H2O

28. 9) 2 C8H O2 →16 CO H2O
10) NH NO → N H2O

29. 9) 2 C8H O2 →16 CO H2O
10) 4 NH NO → 5 N2 + 6 H2O