Question

The atoms present in the products are the same atoms that were present in the reactants because matter is neither created nor destroyed.

Answer 1

Yes — in ordinary chemical reactions the atoms present in the products are the same atoms that were present in the reactants. This is the law of conservation of mass (Lavoisier): atoms are neither created nor destroyed in a chemical reaction, they are only rearranged into new molecules.

What that means in practice
- A balanced chemical equation shows this explicitly: the number of atoms of each element is the same on both sides.
Example: CH4 + 2 O2 → CO2 + 2 H2O
Count atoms: C:1 → 1, H:4 → 4, O:4 → 4.
- The statement assumes a closed chemical system. If gases escape (an open system) it may look like mass is lost, but the atoms still exist (they’ve simply left the container).

Important exceptions
- Nuclear reactions (radioactive decay, fission, fusion) can change one element/atom into another and convert mass to energy (or vice versa) via E = mc^2. In those processes the identity and number of atoms can change.
- Particle physics processes (creation/annihilation) can create or destroy particles, again outside ordinary chemistry.

Short summary: For chemical reactions, yes — atoms are conserved and only their bonds change. Only nuclear or high-energy processes can change atomic identities or create/destroy mass in the strict sense.