When things burn, rust, or fizz, new stuff appears — but where does the matter go? Today you'll learn the rule, then you will predict whether the mass changes.
Before we start — picture a log burning down to a little pile of ash — does that missing stuff just disappear, or go somewhere?
Atoms are the tiny building blocks of all matter. They join together into molecules — like two hydrogen atoms and one oxygen atom making a molecule of water.
In a chemical reaction, the bonds between atoms break and the atoms regroup into brand-new molecules. The starting stuff is the reactants; the new stuff is the products.
Since atoms are only rearranged — never created or destroyed — there is the same number of every atom before and after. So the total mass stays exactly the same. This is the law of conservation of mass.