Law of conservation of mass:
Law of conservation of mass states that “mass can neither be created nor destroyed in a chemical reaction and the total mass of the reactant is always equal to the total mass of the product in a chemical reaction.”
Law of conservation of mass is also known as principle of mass conservation.
A chemical reaction is just separation and reunion of atoms i.e. no new atom or atoms are formed in a chemical reaction. Therefore, mass remains same during a reaction.
Law of conservation of mass Examples:
e.g. 2H2(g) + O2(g) → 2H2O(g)
(2×2) =4g (16X2)=32g 2(18)=36g
(Total mass of Reactant) (Total mass of Product)
N2(g) + 3H2(g) to form 2NH3(g)
Mass before reaction (14×2) = 28g + 3(1×2) = 6g 0 g = 34 g
Mass after reaction 0 g + 0 g 2(14+1×3) = 34 = 34 g
Total moles of atoms before reaction = 2 mole of Nitrogen atoms + 6 mole of Hydrogen atoms = 6 moles of atoms
Total moles of atoms after reaction = 2 mole of Nitrogen atoms + 6 mole of Hydrogen atoms = 6 moles of atoms
As number of moles of atoms remains same in the reaction so mass remains same.