1. The Law of Conservation of Mass
aka The Conservation of Matter
(You just can’t get rid of this stuff.)

2. “Matter cannot be created or destroyed.”
The law of conservation of mass was first described by Antoine Lavoisier (French, )
He demonstrated that you can’t make, or get rid of, matter (atoms).
Lavoisier is considered the father of modern chemistry, among many things.
Click on image for short video (4:21).

3. Atoms can be rearranged into different combinations (called molecules) over and over. And that is what chemical reactions are.
And the same number of atoms in the reactants (before the reaction) will be in the products (after the reaction).
And that is why the mass before is the same as the mass after – in other words, it is conserved.

4. The atoms in molecules can be separated and rearranged over and over, in countless different ways. But they remain the same atoms - they just don’t ever go away.

5. And if it is a “closed system” (meaning nothing can escape), the total mass of the reactants will always equal the total mass of the products.

6. Click for video!

7. Alchemy
For years, people tried to turn a non-precious metal - like lead (Pb) - into a precious metal - like gold (Ag).
Can you now explain why this is not possible?