1. II. Balancing Equations

2. Coefficient  subscript = # of atoms
A. Balancing Steps
1. Write the unbalanced equation.
2. Count atoms on each side.
3. Add coefficients to make #s equal.
Coefficient  subscript = # of atoms
4. Reduce coefficients to lowest possible ratio, if necessary.
5. Double check atom balance!!!

3. B. Helpful Tips Balance one element at a time.
Update ALL atom counts after adding a coefficient.
If an element appears more than once per side, balance it last.
Balance polyatomic ions as single units.
“1 SO4” instead of “1 S” and “4 O”

4. C. Balancing Example 2 Al + CuCl2  Cu + AlCl3 Al Cu Cl 3 3 2 2  1 1
Aluminum and copper(II) chloride react to form copper and aluminum chloride. 2
Al CuCl2  Cu AlCl3 Al Cu Cl 3 3 2
2 
 2
 6
3 
6 
 3

5. Evidence of chemical change
Light
Heat
Formation of gas
Change in color
Formation of a precipitate

6. All chemical reactions
have two parts
Reactants - the substances you start with
Products- the substances you end up with
The reactants turn into the products.
Reactants ® Products

7. Symbols used in equations
the arrow ® separates the reactants from the products
Read “reacts to form”
The plus sign = “and”
(s) after the formula -solid
(g) after the formula -gas
(l) after the formula –liquid
(aq) dissolved in water

8. Balanced Equation Atoms can’t be created or destroyed
All the atoms we start with we must end up with
A balanced equation has the same number of each element on both sides of the equation.

9. ® O + C O C O O C + O2 ® CO2 This equation is already balanced
What if it isn’t already?

10. ® O + C C O O C + O2 ® CO We need one more oxygen in the products.
Can’t change the formula, because it describes what is

11. ® C O O + C O C O Must be used to make another CO
But where did the other C come from?

12. C C O O + O C C O
Must have started with two C
2 C + O2 ® 2 CO

13. Rules for balancing
Write the correct formulas for all the reactants and products
Count the number of atoms of each type appearing on both sides
Balance the elements one at a time by adding coefficients (the numbers in front)
Check to make sure it is balanced.

14. Never Change a subscript to balance an equation.
If you change the formula you are describing a different reaction.
H2O is a different compound than H2O2
Never put a coefficient in the middle of a formula
2 NaCl is okay, Na2Cl is not.

15. Example
H2 + O2
H2O
Make a table to keep track of where you
are at

16. Example
H2 + O2
H2O R P 2 H 2 2 O 1
Need twice as much O in the product

17. Example
H2 + O2 2
H2O R P 2 H 2 2 O 1
Changes the O

18. Example
H2 + O2 2
H2O R P 2 H 2 2 O 1 2
Also changes the H

19. Example
H2 + O2 2
H2O R P 2 H 2 4 2 O 1 2
Need twice as much H in the reactant

20. Example 2
H2 + O2 2
H2O R P 2 H 2 4 2 O 1 2
Recount

21. Example 2
H2 + O2 2
H2O R P 4 2 H 2 4 2 O 1 2
The equation is balanced, has the same
number of each kind of atom on both sides

22. Example R P 4 2 H 2 4 2 O 1 2 2 H2 + O2 ® 2 H2O This is the answer
Not this

23. Examples AgNO3 + Cu ® Cu(NO3)2 + Ag Mg + N2 ® Mg3N2 P + O2 ® P4O10
Na + H2O ® H2 + NaOH
CH4 + O2 ® CO2 + H2O
Pb(NO3)2+ KI  

24. On a separate sheet of paper balance the equations

25. Examples 2AgNO3 + Cu ® Cu(NO3)2 + 2Ag 3Mg + N2 ® Mg3N2
4P + 5O2 ® P4O10
2Na + 2H2O ® H2 + 2NaOH
CH4 + 2O2 ® CO2 + 2H2O