Download Notes-Law of Conservation of Mass

Notes
SPI 0807.9.11
Law of Conservation of Mass
Science
Tennessee SPI Objective:
Recognize that in a chemical reaction the mass of the
Instructions
for of
Students
reactants is equal
to the mass
the products.
1) Make sure you view this presentation in slideshow mode.
(Law of Conservation of Mass: LOCOM)
2) You can find instructions about how to do this by doing a
Google search or by searching
EssentialYouTube.
Question(s)
3)
After
have it in slideshow
mode,
How
doyou
I determine
the number
andpress
typethe
of right-arrow
atoms on each
keyboard
to advance
the presentation.
side of a button
chemical
equationthrough
to confirm
the LOCOM?
4) If you need help, please communicate with your teacher.
Check for Understanding
Model how to count the numbers of atoms on each side of
chemical reactions to confirm the Law of Conservation of Mass.
Notes
SPI 0807.9.11
Law of Conservation of Mass
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
LOCOM
Notes
SPI 0807.9.11
Law of Conservation of Mass
Science
2 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
Example: 2H2 +
O2
Reactants
(Hydrogen & Oxygen)
2H2O
Product
(water)
Notes
SPI 0807.9.11
Law of Conservation of Mass
Science
3 key symbols in chemical equations
(1) Subscript (2) Coefficient (3) Yields Arrow
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
Example: 2H2 +
O2
2H2O
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 2
H 2O
2&1
2 & 2
Four is not equal to three!
F.Y.I.
Balancing Equations:
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 + O2
4
&
2H2O
4&2
2
Six is equal to Six!
Now it demonstrates the law of conservation of mass.
Quick
Review
SPI 0807.9.11
Law of Conservation of Mass
Na + Cl2
Science
2NaCl
(count the atoms on each side)
How many sodium (Na) reactants?
One
How many sodium (Na) products?
Two
How many chlorine (Cl) reactants?
Two
Two
How many chlorine (Cl) products?
Does this demonstrate the law of conservation of mass?
No it does not!
Why? Look at the sodium atoms on each side
Quick
Review
SPI 0807.9.11
Law of Conservation of Mass
2N2 + O2
Science
2N2O
(count the atoms on each side)
How many nitrogen (N) reactants?
Four
How many nitrogen (N) products?
Four
How many oxygen (O) reactants?
Two
Two
How many oxygen (O) products?
Does it demonstrate the law of conservation of mass?
Yes it does!
Why? Same number of atoms on each side
Review
SPI 0807.9.11
Law of Conservation of Mass
Science
Hint: Count the atoms on each side of the arrow
Review
SPI 0807.9.11
Law of Conservation of Mass
Science
Hint: Count the atoms on each side of the arrow
Review
SPI 0807.9.11
Law of Conservation of Mass
Science
Hint:
Count the amounts of reactants and products
Review
SPI 0807.9.11
Law of Conservation of Mass
Science
Hint:
Use substitution: K= 39 grams, O= 32 grams
…so 39 + 32
???
Review
SPI 0807.9.11
Law of Conservation of Mass
Science
Hint:
Count the amounts of reactants and products.