Law of Conservation of Mass
This is by a French scientist Antoine Lavoisier and basically says:
Mass cannot be created or destroyed during any chemical or physical change. This basically means if you don't interfere with a substance or multiple substances (for example remove or add bits of it), and just let it sit there or let it react, then its mass won't change.
In other words, In a chemical reaction, the mass of all the reactants in the beginning will be equivalent with the total mass of all the products at the end of the reaction. This means in a chemical reaction, although products may change form or be altered or rearranged, its total mass will be the same. Armed with this, we can now balance equations to perform Reaction Stoichiometry, which helps chemists calculate how much of each products will be produced.
Another thing we could do is to work out how much of something is produced. (This is not often used though - but great for checking anyway!) Exercise:
If heating 10 grams of CaCO3 produces 4.4g of CO2 and, how many grams of CaO will be produced?
First let's write down the equation:
CaCO3 -> CO2 + CaO As you can see, it's already balanced, so let's add in the mass of each side:
CaCO3 -> CO2 + CaO
10g 4.4g ?g
We know that both sides must be equal to 10g, so 10-4.4=5.6 which means there will be 5.6g of CaO produced.
