2. Writing chemical Reactions
Use a Periodic Table to determine what each of these symbols stand for: Record the symbol and what it stands for. Au Pb Ag Sn
You can find free printable Periodic Tables for your class here: Fe Al Ca C
(c) S. Coates 2012

3. Writing chemical ReactionsAu Pb Ag Sn
Gold
Lead
Silver
Tin Fe Al Ca C
Iron
Calcium
Carbon
Aluminum
(c) S. Coates 2012

4. Writing chemical Reactions There are TWO hydrogen atoms
You have already seen many chemical formulas…
H2O
What does the “H” stand for?
What does the “O” stand for?
What does the little “2” stand for?
Hydrogen
*This information should be added to the graphic organizer
Oxygen
There are TWO hydrogen atoms
(c) S. Coates 2012

5. Compound Formula Aspirin C9H8O4 Bleach NaClO Sugar C12H22O11 Rust
Here are some familiar items. Use a Periodic Table of the Elements to record what these compounds are made of…
Compound
Formula
Aspirin
C9H8O4
Bleach
NaClO
Sugar
C12H22O11
Rust
Fe2O3
Rubbing Alcohol
C3H8O
Lowercase “L”, not an I.
(c) S. Coates 2012

6. Understanding Written Equations
Writing chemical Reactions
Compound
Formula
Made of….
Aspirin
C9H8O4
9 Carbons, 8 Hydrogens, and 4 Oxygens
Bleach
NaClO
1 Sodium, 1 Chlorine, 1 Oxygen
Sugar
C12H22O11
12 Carbons, 22 Hydrogens, and 11 Oxygens
Rust
Fe2O3
2 Irons, 3 Oxygens
Rubbing Alcohol
C3H8O
3 Carbons, 8 Hydrogens, and 1 Oxygen
(c) S. Coates 2012

7. Writing chemical Reactions
Structure of a chemical equation:
Every chemical equation is written
THE SAME WAY…
Reactant + Reactant  Product + Product
Sometimes there are more than 2 reactants.
Sometimes there is only 1 reactant.
Sometimes there are more than 2 products.
Sometimes there is only 1 product.
(c) S. Coates 2012

8. Writing chemical Reactions
See if you can answer the following questions for this chemical reaction:
CaCO CaO + CO2
(Heated)
How many reactants are there?
What is/are the reactant(s)?
How many products are there?
What is/are the product(s)?
(c) S. Coates 2012

9. Writing chemical Reactions
CaCO CaO + CO2
* Notice that the atoms we began with are the same atoms we end with, just in a different order!
(Heated) Ca C O O O 3 2
(c) S. Coates 2012

10. Understanding chemical Reactions
The amount of matter involved in a chemical reaction does not change.
The total mass of the reactants MUST EQUAL the total mass of the products.
We call this principle Conservation of Mass.
(c) S. Coates 2012

11. Writing chemical Reactions
How do you know if the mass of the products is equal to the mass of the reactants?
Subscript Numbers!
If you add up the NUMBER of EACH element on the reactant side and compare it to the NUMBER of the SAME element on the product side you can tell if the mass of the reactants is equal to the mass of the products.
CaCO3  CaO + CO2
(c) S. Coates 2012

12. Understanding chemical Reactions Yes! The masses are equal!
For example:
Na + Cl  NaCl
1. Count up the number of Na and Cl atoms on the reactant side.
Na = 1 Cl = 1
2. Count up the number of Na and Cl atoms on the product side.
3. Compare the numbers. Are they the same? If so then the mass of the reactants and the products is equal.
Yes! The masses are equal!
(c) S. Coates 2012

13. Understanding chemical Reactions
Here’s another:
Fe2 + S2  Fe2S2
1. Count up the number of Fe and S atoms on the reactant side.
Fe = 2 S = 2
2. Count up the number of Fe and S atoms on the product side.
3. Compare the numbers. Are they the same? If so then the mass of the reactants and the products is equal.
Yes! The masses are equal!
(c) S. Coates 2012

14. Understanding chemical Reactions That makes this equation “unbalanced”
But what if the numbers are NOT equal?
H2 + O2  H2O
1. Count up the number of H and O atoms on the reactant side.
H = 2 O = 2
2. Count up the number of H and O atoms on the product side.
H = 2 O = 1
3. Compare the numbers. Are they the same?
NO! The masses are NOT equal!
That makes this equation “unbalanced”
(c) S. Coates 2012

15. Understanding chemical Reactions That makes this equation “unbalanced”
Try another one…
CO2 + H2O  C6H12O6 + O2
1. Count up the number of C, H, and O atoms on the reactant side.
C = 1 H = 2 O = 3
2. Count up the number of H and O atoms on the product side.
C = 6 H = 12 O = 8
3. Compare the numbers. Are they the same?
NO! The masses are NOT equal!
That makes this equation “unbalanced”
(c) S. Coates 2012

16. Understanding chemical Reactions
What do you do when an equation is “unbalanced?”
That’s something you’ll be learning in high school Chemistry.
For now you just need to understand whether and equation is balanced or unbalanced.
(c) S. Coates 2012

17. Understanding chemical Reactions
Let’s summarize:
Chemical reactions can cause changes in properties and changes in energy.
Chemical reactions occur when the bonds between atoms break, or when new bonds between atoms are formed.
We can write equations for chemical reactions by using symbols
Chemical reactions must follow the Law of Conservation of Mass.
(c) S. Coates 2012