the law of conservation of matter. we’ve talked about changes in matter… the evaporation of a...
TRANSCRIPT
The Law of The Law of Conservation of Conservation of
MatterMatter
We’ve talked about changes in matter…
• The evaporation of a puddle of water
• Rust forming on a metal fence
PHYSICAL
CHEMICAL
HOWEVER…
• No matter is created or destroyed by such changes!
• The total amount of matter remains constant.
How did scientists come up with this law?• Just like we did with the
vinegar and baking soda in a bag!
• They measured the mass of the reactants (vinegar and baking soda) and then, after the reaction took place, they measured the mass of the products (reactants + carbon dioxide)
The Law of Conservation of Matter
• During a chemical reaction, matter cannot be created or
destroyed.
• Even though the matter may change from one form to another, the same number of atoms exists before and
after the change takes place!
Since the overall mass of the matter does not
change…• The mass of the reactants – the
substances there before the reaction occurs – must equal the mass of the product – the substances there after the reaction takes place.
Mass of Reactants
Mass of Products
An Example of the L.C.M.
• Test tube containing lead lead nitratenitrate is placed upright in a flask that contains potassium iodidepotassium iodide.
• What are these?– REACTANTS!
• They don’t mix!
• A stopper is put in place to create a closed system – an environment where matter cannot enter or escape.
• The mass of the system is found.
• After the mass is found, the system is turned upside down so the lead nitrate can mix with the potassium iodide.
• They create lead iodide and potassium nitrate.
•Although the matter changed in form, the total mass of the system remains unchanged.
The Formation of Rust
• Iron– Hard, gray-colored
metal
• Rust– Flaky, orange-red
solid
When iron reacts with oxygen in the air, they form rust or
IRON OXIDE.
•This is written as:Iron + Oxygen Iron Oxide
Fe Fe
Fe Fe
RE
AC
TAN
TS
Each made of TW
O
oxygen atoms
O2
O2 O2
PRODUCT
Fe2O3 Fe2O3
TAKE A LOOK AT
THE NUMBERS
How many Iron molecules?
How many Oxygen
molecules?
What about the
PRODUCT?
All Chemical Reactions follow the Law of
Conservation of Matter
• With Iron Oxide, the MASS STAYS THE SAME!– The total number of iron atoms and
oxygen atoms in the reactants is the same as that in the product.
– The atoms were just rearranged!• No new atoms were created and none were
destroyed!
Determining the Mass of Reactants and
Products• REMEMBER: The mass of the
reactants is always equal to the mass of the products.
Mass of Reactants
Mass of Products
Example: Tin Fluoride
• Tin + hydrogen fluoride -> tin fluoride + hydrogen
• What’s the total mass of the reactants?– 158.72 g
• So what should the mass of the products be?– 158.72 g
118.7 g
40.02 g
• Tin + hydrogen fluoride -> tin fluoride + hydrogen
• If we know the mass of the tin fluoride, can we figure out how much hydrogen was produced?– Subtract the mass of one product from the
total mass.
Total Mass of Reactants: 158.72 g
156.71 g
2.01 g
ANY QUESTIONS?