Question

Justify: "The total mass of the products remains equal to the total mass of the reactants during a chemical reaction."

Answer 1

Dalton's atomic theory:

• According to Dalton's atomic theory, “Atoms can neither be created nor be destroyed”.
• Therefore, in a chemical reaction, the atoms only rearrange themselves to form products.
• Thus, the total mass of the products remains equal to the total mass of reactants during a chemical reaction.

Example:

1. When Calcium carbonate (${\mathrm{CaCO}}_3$) undergoes decomposition it gives Calcium oxide ($\mathrm{CaO}$) and Carbon dioxide (${\mathrm{CO}}_2$).
2. ${\mathrm{CaCO}}_3\left(\mathrm{s}\right)\stackrel{∆}{\to }\mathrm{CaO}\left(\mathrm{s}\right)+{\mathrm{CO}}_2\left(\mathrm{g}\right)$
3. The reactant (left side) here is made up of 1 calcium atom, 1 carbon atom and 3 oxygen atoms.
4. The products (right side), we have 1 atom of Calcium in $\left(\mathrm{CaO}\right)$, 1 atom of carbon in $\left({\mathrm{CO}}_2\right)$ and 3 atoms of oxygen.
5. This shows that there is no change in the mass during the decomposition of Calcium carbonate and mass remains conserved.