1. Balancing Act

2. Atoms are not CREATED or DESTROYED during a chemical reaction
Atoms are not CREATED or DESTROYED during a chemical reaction. This is the LAW OF CONSERVATION OF MASS.
There must be the same number of atoms on each side of the equation.
massbegin = massend

3. Law of Conservation of Mass
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.

4. reactants product Conservation of Mass
mass of reactants = mass of products

5. Iron + Oxygen -----> Rust mass reactants = mass products
Conservation of Mass
Iron + Oxygen -----> Rust
100 g + ? g > 143g
mass reactants = mass products
What is the mass of Oxygen?

6. What is a chemical equation?
Chemical equation - Describes a chemical change.
Parts of an equation:
Reactant
Product
2Ag + H2S
Ag2S + H2
Reaction symbol

7. Reactants and Products
Reactant - The chemical(s) you start with before the reaction.
Product - The new chemical(s) formed by the reaction.

8. To balance the chemical equation, you must place
COEFFICIENTS in front of the chemical formulas in the equation.
A coefficient is a number placed in front of a chemical formula in an equation that shows how many atoms are involved in a reaction.
(Multiplier)
Example: 2MgO (2 is the coefficient)
There are 2 Magnesium and 2 Oxygen atoms

9. Subscripts
A subscript is a number written to the right of a chemical symbol and slightly below it. It tells how many atoms of that element.
Example: H2O (2 is the subscript)
This molecule has
2 hydrogen and 1 oxygen.
You cannot ADD or CHANGE subscripts!

10. Subscripts and Coefficients
Subscript - shows how many atoms of an element are in a molecule.
EX: H2O
2 atoms of hydrogen (H)‏
1 atom of oxygen (O)‏
Coefficient - shows how many molecules there are of a particular chemical.
EX: 3 H2O
Means there are 3 water molecules.

11. Conservation of Mass

12. A Chemical Reaction
2H2 + O2  2H2O

13. reactants product Conservation of Mass
mass of reactants = mass of products

14. 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

15. A Balanced Equation CH4 + 2O2  CO2 + 2H2O Reactant Side Product Side
1 carbon atom
4 hydrogen atoms
4 oxygen atoms
1 carbon atom
4 hydrogen atoms
4 oxygen atoms

16. What chemical equation is this?
Conservation of Mass
What chemical equation is this?

17. BALANCING EQUATIONS STEPS
1. Determine the number of atoms for each element.
2. Pick an element that is not equal on both sides of the equation.
3. Place a coefficient in front of the formula with that element and adjust your counts.
4. Continue adding coefficients to get the same number of atoms of each element on each side.

18. 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 chem. formulas...NEVER in the middle of a formula.
A few 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.

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

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

21. Balancing Chemical Equations Practice

22. Example 1

23. Example 2

27. Balancing Equations 4 6 7 2 Balance the following equation:
C2H6 + O2  CO2 + H2O 4 6 7 2

28. Balancing Equations 2 3 4 Balance the following equation:
Fe + O2  Fe2O3 2 3 4

29. Conservation of Mass Videos
Brain Pop
Conservation of Mass
mance
science 29

30. Balancing Act Homework

31. Balancing Act Homework ANSWERS

32. Balancing Act Homework ANSWERS

33. Balancing Act Homework

34. Balancing Act Homework ANSWERS

35. Balancing Act Homework ANSWERS

36. Balancing Act Homework ANSWERS