Chemistry (NTSE/Olympiad)  

3. Atoms & Molecules

Law of Conservation of Mass

The laws of chemical combination played a significant role in the development of Dalton’s atomic theory of matter.
There are two important laws of chemical combination.
(A) Law of conservation of mass
Law of conservation of mass was given by Lavoisier in 1774. According to the law of conservation of mass : Matter is neither created nor destroyed in a chemical reaction. The substances which combine together in a chemical reaction are known as ‘reactants’ whereas the new substances formed as a result of chemical reaction are called ‘products’. The law of conservation of mass means that in a chemical reaction, the total mass of products is equal to the total mass of reactants. There is no change in mass during a chemical reaction.
Example. Lavoisier showed that when mercuric oxide was heated, it produced free mercury and oxygen. The sum of masses of mercury and oxygen was found to be equal to the mass of mercuric oxide

Solution. Mass of the reactant = 100 g
Mass of the products = 92.6 + 7.4 g = 100.0 g = 100 g
Since the total mass of the products formed is equal to the total mass of the reactants undergoing reaction, so the data is in agreement with low of conservation of mass.

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