The Conservation of Mass is really important when we balance chemical equations.

It means that in a closed system, the mass of the things we start with (called reactants) is the same as the mass of what we end up with (called products).

Here’s how it works:

• Every atom in the reactants must match with an atom in the products.

For example, think about this reaction:
$2H_2 + O_2 \rightarrow 2H_2O$.

We start with 4 hydrogen atoms and 2 oxygen atoms.

After balancing, we still have the same amount: 4 hydrogen and 2 oxygen.

So, remember, nothing is lost in this process; everything is just rearranged!