1. Day 18 Balancing Chemical Equations
Sci 10 Chemistry

2. 5H2 Review What number represents the Coefficient? _____
What number represents the Subscript? _____
What element is represented by the letter "H"? _____
How many "H's" do you have? _____

3. Counting Atoms
How many of each type of atom are present in the compounds below?
H2SO4
CaCl2
4NaF
2KNO3
3K2SO4
2Mg3(PO4)2
Type of Atom
# of Atoms

4. Law of Conservation of Mass
Law of conservation of mass: mass of products = mass of reactants
Video:
the # of atoms of each type in the reactants = the # of atoms of each type in the products
Matter can’t be created or destroyed: atoms can’t be gained or lost during a chemical reaction
A B → C D
“reacts with”
Reactants
Products
“produces/ gives”

5. Balancing Chemical Equations
Skeleton equation: CH4(g) + O2(g)  CO2(g) + H2O(l)
The skeleton equation needs coefficients to balance both sides.
Balanced equation: CH4(g) + 2O2(g)  CO2(g) + 2H2O(l)
Subscripts
show the # of atoms *YOU CANNOT CHANGE THESE TO BALANCE AN EQUATION
State of matter
(aq) = aqueous/dissolved in water
(s) = solid
( l ) = liquid
(g) = gas
Coefficients
indicate the ratio of compounds in the reaction
here, there is twice as much NO and NO2 than there is O2 5

6. Types of Chemical Equations
Word Equation (words only, no formulas):
Methane + oxygen  carbon dioxide + water
Skeleton Equation (formulas, but not balanced):
CH4(g) + O2(g)  CO2(g) + H2O(l)
Balanced Equation:

7. Remember:
You can only change the coefficients (the number in front) to balance
You can not have coefficients that are fractions
Double check to make sure coefficients can’t be reduced

8. Examples
Hg + O2  HgO
Aluminum reacts with oxygen to form aluminum oxide.
CaO + H2O  Ca(OH)2

9. Strategies for Balancing Equations
Balance chemical equations by following these steps:
Trial and error will work, but can be very inefficient
Balance compounds first, elements last
Balance one compound at a time
Only add coefficients; NEVER change subscripts!
If H and O appear, attempt to balance them LAST
Polyatomic ions (such as SO42–) can be balanced as a whole group. They don’t break apart!
Always double-check after you think you are finished! 9

10. More examples Balance the following:
__ N2 (g) + ___ H2 (g) → ___ NH3 (g)
__ N2 (g) + _3_ H2 (g) → _2_ NH3 (g)
__ Fe (s) + ___ H2SO4 (aq) → ___ H2 (g) + Fe2(SO4)3 (aq)
2_ Fe (s) + _3_ H2SO4 (aq) → _3_ H2 (g) + Fe2(SO4)3 (aq)

11. Balancing Word Equations
Write the skeleton equation. Remember to ensure ionic compounds have a neutral charge (+ and – charges must add to zero)
Then balance
Check coefficients for common factors. If yes, reduce them.

12. Try It! sodium + chlorine  sodium chloride
iron (II) oxide  iron + oxygen
methane + oxygen  carbon dioxide + water
copper (I) oxide  copper + oxygen

13. Try balancing these: Stop & Think! Fe + Br2  FeBr3
CaCl2 + Na  NaCl + Ca
Sn(NO2)4 + K3PO4  KNO2 + Sn3 (PO4)4
C2H6 + O2  CO2 + H2O

14. To Do: Day 18 Practice 1 Text: p.133 #13, 18 p.137 #8, 9, 11-18