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1. Recap

2. Atomic Mass

3. Atomic Mass Unit

4. Molecular Mass

5. Formula Mass

6. Avogadro’s Number

7. Tower of Power

8. Fit it Right

9. FORMULA

10. Equation

11. Balance

12. Balancing Chemical Equations
Physical Science Week 6

13. Objectives
Learning Competency
Learning Competency
Balance chemical equations
Identify parts of an equation
Determine the limiting reactant in a
reaction and calculate the amount of
product formed (S11/12PS-IIIh-27)

14. What is a chemical equation?
• Chemical equation - Describes a chemical change.
• Parts of an equation:
2Ag + H
2Ag + H2
2S
S Ag
Ag2
2S + H
S + H2
2
Reactant Product

15. Reactants and Products
•Reactant - The chemical(s) you start
with before the reaction.
• Written on left side of equation.
•Product - The new chemical(s) formed
by the reaction.
• Right side of equation.

16. Subscripts and Coefficients
• Subscript - shows how many atoms of an
element are in a molecule.
• EX: H2
O
• 2 atoms of hydrogen (H) ;
1 atom of oxygen (O)
• Coefficient - shows how many molecules there
are of a particular chemical.
• EX: 3 H2
O
• Means there are 3 water molecules.

17. A Chemical Reaction
• 2H2
+ O2
 2H2
O

18. Law of Conservation of Mass
• In a chemical reaction, matter is neither
created nor destroyed.
• In other words, the number and type of
atoms going INTO a reaction must be the
same as the number and type of atoms
coming OUT.
• If an equation obeys the Law of
Conservation, it is balanced.

19. An Unbalanced Equation
• CH4 + O2  CO2 + H2O
Reactant Side Product Side
1 carbon atom
4 hydrogen atoms
2 oxygen atoms
1 carbon atom
2 hydrogen atoms
3 oxygen atoms

20. A Balanced Equation

CH4
+ 2O2
 CO2
+ 2H2
O
Reactant Side Product Side
1 carbon atom
4 hydrogen atoms
4 oxygen atoms
1 carbon atom
4 hydrogen atoms
4 oxygen atoms

21. Rules of the Game
1. Matter cannot be created or destroyed.
2. Subscripts cannot be added, removed,
or changed.
3. You can only change coefficients.
4. Coefficients can only go in front of
chemical formulas...NEVER in the middle
of a formula.

22. Extra Tips…
Try balancing big formulas first; save free
elements for last.
If the same polyatomic ion appears on
both sides of the equation, it’s usually okay
to treat it as one unit.
There is no one particular way to balance
equations. Some equations are harder to
balance than others and might require
some creativity to solve.

23. Balancing Equations
Balance the following equation by adjusting
coefficients.
reactants products
N
H
N
N2
2 + H
+ H2
2

 NH
NH3
3
2
2
1
3
2
2
2
6
3
3
6

24. Balancing Equations
• Balance the following equation by adjusting
coefficients.
KClO
KClO3
3

 KCl + O
KCl + O2
2
reactants products
K
Cl
O
1
1
1
1
3 2
3
3
2
2
2
2
6 6
2
2
2
2

25. Balancing Equations
•Balance the following equation:
• C2
H6
+ O2
 CO2
+ H2
O
4
4 6
6
7
7
2
2

26. Balancing Equations
•Balance the following equation:
• Fe + O2
 Fe2
O3
2
2
3
3
4
4

27. Seatwork