1. Balancing Chemical Equations
What goes in must come out!

2. LecturePLUS Timberlake
Physical Properties
color
melting point
boiling point
electrical conductivity
specific heat
density
state (solid, liquid, or gas)
LecturePLUS Timberlake

3. LecturePLUS Timberlake
Physical Change
Changes in physical properties
melting
boiling
condensation
No change occurs in the identity of the substance
Example:
Ice , rain, and steam are all water
LecturePLUS Timberlake

4. LecturePLUS Timberlake
Chemical Change
Atoms in the reactants are rearranged to form one or more different substances
Old bonds are broken; new bonds form
Examples:
Fe and O2 form rust (Fe2O3)
Ag and S form tarnish (Ag2S)
LecturePLUS Timberlake

5. LecturePLUS Timberlake
Learning Check E1
Classify each of the following as a
1) physical change or 2) chemical change
A. ____ a burning candle
B. ____ melting ice
C. ____ toasting a marshmallow
D. ____ cutting a pizza
E. ____ polishing silver
LecturePLUS Timberlake

6. LecturePLUS Timberlake
Solution E1
Classify each of the following as a
1) physical change or 2) chemical change
A. __2__ a burning candle
B. __1_ melting ice
C. __2__ toasting a marshmallow
D. __1__ cutting a pizza
E. __2__ polishing silver
LecturePLUS Timberlake

7. LecturePLUS Timberlake
Chemical Reaction
A process in which at least one new substance is produced as a result of chemical change.
LecturePLUS Timberlake

8. LecturePLUS Timberlake
Learning Check E3
12 oz of dough, 4 oz mushrooms, 12 slices pepperoni, 8 oz cheese and 5 oz tomato sauce are used to make a pizza. Write a recipe in words for putting together a pizza.
How would you write the recipe as an equation?
LecturePLUS Timberlake

9. LecturePLUS Timberlake
Solution E3
Example: Combine 12 oz dough + 4 oz mushrooms + 12 slices pepperoni + 8 oz cheese + 5 oz tomato sauce and heat 30 minutes at 350°C to produce 1 pizza
12 oz dough + 4 oz mshrm
+ 12 pep + 8 oz chse pizza
+ 5 oz tom sauce
LecturePLUS Timberlake

10. Balancing Chemical Equations
Balancing a chemical equation is much like the work of an accountant who has to show every penny that comes in and where it has gone to.

11. Objectives Learn the steps to balancing chemical equations.
Take notes to help you understand.
Test yourself with a set of equations to balance.
Enter your own equations to see if they balance.

12. Law of Conservation of Mass You need to remember this law!
The Law of Conservation of Mass states: that mass is neither created nor destroyed in any chemical reaction. Therefore balancing of equations requires the same number of atoms on both sides of a chemical reaction.
The number of atoms in the Reactants must equal the Number of atoms in the Products

13. Chemical Equations
Lavoisier, 1788
Because of the principle of the Conservation of Matter,
an equation must be balanced.
It must have the same number of atoms of the same kind on both sides.

14. Law of Conservation of Mass
The mass of all the reactants (the substances going into a reaction) must equal the mass of the products (the substances produced by the reaction).
Reactant + Reactant = Product

15. A simple equation, such as the synthesis of Iron (II) sulfide,
iron + sulfur Iron (II) sulfide
Fe + S FeS
Note that in a chemical equation, by convention, we use the arrow “ " instead of the equals “ = ".

16. The last stage is to put in state of matter symbols, (s, l, g, aq), as appropriate (solid, liquid, gas, aqueous or dissolved in water)
Fe(s) + S(s) FeS(s)

17. Balancing Equations 2 3
___ Al(s) + ___ Br2(l) ---> ___ Al2Br6(s)

18. Steps to Balancing a Chemical Equation
Write all reactants on the left and all products on the right side of the equation arrow. Make sure you write the correct formula for each element
2. Use coefficients in front of each formula to balance the number of atoms on each side.

19. Steps to Balancing a Chemical Equation
3. Multiply the coefficient of each element by the subscript of the element to count the atoms. Then list the number of atoms of each element on each side.
4. It is often easiest to start balancing with an element that appears only once on each side of the arrow. These elements must have the same coefficient. Next balance elements that appear only once on each side but have different numbers of atoms. Finally balance elements that are in two formulas in the same side.

20. Re-cap of steps from rule 4:
Balance elements that appear only once on each side of the arrow.
Next balance elements that appear only once on each side but have different numbers of atoms.
Finally balance elements that are in two formulas in the same side.

21. Balancing Chemical Equations
An easier way

22. First you need an equation with the correct “formulae” ………
First you need an equation with the correct “formulae” ………. You’ll probably be given this in the question
Just like this one
Mg + O2  MgO
Then all you do is list the atoms that are involved on each side of the arrow
Mg + O2  MgO Mg O Mg O

23. Mg + O2  MgO Mg + O2  MgO 2 Then start balancing:
[1] Just count up the atoms on each side
Mg + O2  MgO Mg O 1 1 2 1
[2] The numbers aren’t balanced so then add “BIG” numbers to make up for any shortages
Mg + O2  MgO Mg O 1 2 2 2 2
And adjust totals

24. WE SAY THAT THE EQUATION IS BALANCED!!
But the numbers still aren’t equal, so add another “BIG” number 2
Mg + O2  MgO Mg O 1 2 2
And adjust totals again
NOW BOTH SIDES HAVE EQUAL NUMBERS OF ATOMS
WE SAY THAT THE EQUATION IS BALANCED!!

25. Try to balance these equations using the same method:
[1] Na + Cl2  NaCl
[2] CH4 + O2  CO2 + H2O
[3] Li + HNO3  LiNO3 + H2
[4] Al + O2  Al2O3

26. How did you get on??
Here are the answers:
[1] 2 Na + Cl2  2 NaCl
[2] CH O2  CO H2O
[3] 2 Li + 2 HNO3  2 LiNO3 + H2
[4] 4 Al + 3 O2  2 Al2O3
HOPE YOU’VE GOT THE IDEA… REMEMBER TO CHECK THAT YOU CAN DO ELECTROLYSIS EQUATIONS TOO

27. Example NH3 + O2 NO + H2O Reactants Products
N appears once on both sides in equal numbers, so the coefficient for NH3 is the same as for NO.

28. Example: NH3 + O NO + H2O
Next look at H which appears only once on each side but has different numbers of atoms, 3 on the left and 2 on the right. The least common multiple of 3 and 2 is 6, so rewrite the equation to get 6 atoms of H on both sides:
2NH3 + O NO + 3H2O

29. Example: 2NH3 + O NO + 3H2O
There are 2 oxygen atoms on the left and 5 on the right — the least common multiple of 2 and 5 is 10, so rewrite the equation as:
2NH3 + 5O NO + 6H2O

30. Now count the atoms on each side:
2NH3 + 5O NO + 6H2O
Write them out keeping them on the appropriate side of the chemical equation
2 N (nitrogen atoms) N (nitrogen atoms)
6 H (hydrogen atoms) H (hydrogen atoms)
10 O (oxygen atoms) O (oxygen atoms)
This shows the equation not to be balanced “YET”

31. Check the number again:
If you double the N and H on the left the equation will be balanced:
4NH3 + 5O NO + 6H2O

32. Double-check: 4NH3 + 5O2 4NO + 6H2O The equation is Balanced
4 N (nitrogen atoms) 4 N (nitrogen atoms)
12 H (hydrogen atoms) 12 H (hydrogen atoms)
10 O (oxygen atoms) 10 O (oxygen atoms)
The equation is Balanced

33. Balancing Practice
For more help go to:
For some fun balancing equations go to: