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.

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!

Law of Conservation of MassLaw of Conservation of Mass

Total mass of reactants =

Total mass of productsAntoine Lavoisier

Mass is neither created nor destroyed during chemical or physical reactions.

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

REAC

TANT

S

Each made of TWO

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

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)

ANY QUESTIONS?