1. The Law of Conservation of Matter

2. We’ve talked about changes in matter…
The evaporation of a puddle of water
Rust forming on a metal fence
PHYSICAL
CHEMICAL

3. HOWEVER… No matter is created or destroyed by such changes!
The total amount of matter remains constant.

4. 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!

5. 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

6. An Example of the L.C.M.
Test tube containing lead nitrate is placed upright in a flask that contains potassium iodide.
What are these?
REACTANTS!
They don’t mix!

7. 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.

8. 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.

9. Although the matter changed in form, the total mass of the system remains unchanged.

10. 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

11. ANY QUESTIONS?