1. Notes Science Tennessee SPI Objective:
Law of Conservation of Mass
Notes
Science
Tennessee SPI Objective:
Recognize that in a chemical reaction the mass of the reactants is equal to the mass of the products.
(Law of Conservation of Mass: LOCOM)
Essential Question(s)
How do I determine the number and type of atoms on each
side of a chemical equation?
I Can Statement
I can count the numbers of atoms on each side of chemical reactions.
Success Criteria
I can prove that I understand LOCOM by counting the number of atoms on each side of chemical reactions.

2. LOCOM Notes Science Tennessee SPI Objective:
Law of Conservation of Mass
Notes
Science
Tennessee SPI Objective:
Recognize that in a chemical reaction the mass of the reactants is equal to the mass of the products
(Law of Conservation of Mass: LOCOM)
No atoms are created or destroyed during chemical reactions
So no mass is
created or destroyed
This is called the
Law of
Conservation of Mass
LOCOM

3. Law of Conservation of Mass Two Parts of Chemical Equations
SPI
Law of Conservation of Mass
Notes
Science
Two Parts of Chemical Equations
(1) Reactants
(2) Products
Reactants: chemicals you start with in a reaction
Products: chemicals you end up with in a reaction
2H2 + O H2O
Reactants
(Hydrogen & Oxygen)
Product
(water)

4. Law of Conservation of Mass Three key symbols in chemical equations
SPI
Law of Conservation of Mass
Notes
Science
Subscript: small number below & to the right of a chem symbol
reveals the number of atoms
Coefficient: big number in front of a chemical symbol or formula
(tells you to multiply)
Yields Arrow: always points towards the products
2H2 + O H2O
Three key symbols in chemical equations
(1) Subscript
(2) Coefficient
(3) Yields Arrow

5. H2 + O2 H2O All chemical reactions always obey the…
…Law of Conservation of Mass
Atoms are never created or destroyed in a chemical reaction
… they are just rearranged.
Wrong Example: Look at the unbalanced equation shown below.
It is written incorrectly.
It DOES NOT obey this law.
Therefore it is impossible for this reaction to occur like this.
(count the atoms on each side of the equation)
H2 + O H2O
2 & 2
2 & 1
Four is not equal to three!

6. 2H2 + O2 2H2O F.Y.I. Balancing Equations: 4 & 2 4 & 2
Note: You will learn about this in more detail in High School.
You make the amount of reactants equal the amount of products.
We use coefficients to do this.
Example: Here is the same equation from the previous slide, but
now I have balanced it by placing coefficients.
(count the atoms on each side of the equation)
2H2 + O H2O
4 & 2
4 & 2
Six is equal to Six!
Now it demonstrates the law of conservation of mass.

7. Na + Cl2 2NaCl Science Quick Review How many sodium (Na) reactants?
SPI
Law of Conservation of Mass
Science
Na + Cl NaCl
How many sodium (Na) reactants?
How many sodium (Na) products?
How many chlorine (Cl) reactants?
How many chlorine (Cl) products?
Does this demonstrate the law of conservation of mass?
(count the atoms on each side)
One
Two
Two
Two
No it does not! (What is wrong with it?)
Note: Look at the sodium atoms on each side

8. 2N2 + O2 2N2O Science Quick Review How many nitrogen (N) reactants?
SPI
Law of Conservation of Mass
Science
2N2 + O N2O
How many nitrogen (N) reactants?
How many nitrogen (N) products?
How many oxygen (O) reactants?
How many oxygen (O) products?
Does it demonstrate the law of conservation of mass?
(count the atoms on each side)
Four
Four
Two
Two
Yes it does! (Count the atoms)
Why? Same number of atoms on each side

9. Science Review Hint: Count the atoms on each side of the arrow
SPI
Law of Conservation of Mass
Review
Science
Six
Three
Six
Six 2 4 2 1 4 2 4 2
Hint: Count the atoms on each side of the arrow

10. Science Review Hint: Count the atoms on each side of the arrow
SPI
Law of Conservation of Mass
Review
Science
Two
Four
Eight
Eight 1 1 2 2 2 6 2 6
Hint: Count the atoms on each side of the arrow

11. Science Review Hint: Count the amounts of reactants and products
SPI
Law of Conservation of Mass
Review
Science
Reactants: 2g + 4g = 6g
Products: 6g
Hint:
Count the amounts of reactants and products

12. Law of Conservation of Mass
SPI
Law of Conservation of Mass
Review
Science
Hint:
Use substitution: K= 39 grams, O= 32 grams
…so ???

13. Science Review Hint: Count the amounts of reactants and products.
SPI
Law of Conservation of Mass
Review
Science
Reactants: 4g + 3g = 7g
Products: 7g
Reactants: 5g + 5g = 10g
Products: 20g + 5g = 25g
Hint:
Count the amounts of reactants and products.