* The Law of Conservation of Mass: This fundamental law states that matter cannot be created or destroyed in ordinary chemical reactions. This means the total mass of reactants must equal the total mass of products.
* Moles Represent Quantity: Moles are a unit of measurement for the amount of substance. A mole of one substance contains the same number of particles (atoms, molecules, etc.) as a mole of another substance.
* Balancing Equations: Balancing chemical equations ensures that the number of atoms of each element on the reactant side equals the number of atoms of that element on the product side. Since moles represent the amount of substance, this means that the number of moles of reactants must equal the number of moles of products.
Example:
Consider the balanced equation for the combustion of methane:
```
CH4 + 2O2 -> CO2 + 2H2O
```
* Reactants: 1 mole of methane (CH4) and 2 moles of oxygen (O2)
* Products: 1 mole of carbon dioxide (CO2) and 2 moles of water (H2O)
We can see that the total number of moles of reactants (1 + 2 = 3) equals the total number of moles of products (1 + 2 = 3).
Important Note: While moles are conserved, the number of molecules or atoms may not be. For instance, in the methane combustion example, we have 1 molecule of methane and 2 molecules of oxygen reacting to form 1 molecule of carbon dioxide and 2 molecules of water.
