Question

Explain law of conservation of mass with example.

Answer 1

The law of conservation of mass itself indicates its meaning. According to this mass of product equals the mass of reactants. We cannot create the mass but we can convert it into another form.

Complete step by step solution:
According to the law of conservation of mass, mass cannot be created or destroyed. Only the conversion of mass from one form to another form is possible.
Let’s take a chemical reaction of silver chloride with sodium nitrate. The reaction is represented as follows:
${\text{AgCl}}\,{\text{ + }}\,{\text{NaN}}{{\text{O}}_{\text{3}}}\, \to \,{\text{AgN}}{{\text{O}}_{\text{3}}}\,{\text{ + }}\,{\text{NaCl}}$
By the reaction of silver chloride with sodium nitrate, the silver nitrate and sodium chloride forms.
The molar mass of silver chloride is $143.32\,{\text{g/mol}}$.
The molar mass of sodium nitrate is $84.99\,{\text{g/mol}}$.
The molar mass of silver nitrate is $169.87\,{\text{g/mol}}$.
The molar mass of sodium chloride is $58.44\,{\text{g/mol}}$.
Now we will subtract the sum of the mass of products from the sum of the mass of reactants to determine the mass loss as follows:
${\text{Mass}}\,{\text{loss = }}\,\left( {169.87\, + \,58.44} \right)\, - \,\left( {143.32\,{\text{ + }}\,84.99\,} \right)\,$
${\text{Mass}}\,{\text{loss = }}\,228.31\, - \,283.31\,$
${\text{Mass}}\,{\text{loss = 0}}$
So, the mass loss during the reaction of silver chloride with sodium nitrate is zero. It means all the mass of the reactant is converting into the product.

Note:
The number of moles can be changed but not the overall mass. For example, consider the decomposition of calcium carbonate into calcium oxide and carbon dioxide. One mole calcium carbonate gives one-mole calcium oxide and one-mole carbon dioxide so, two moles of products are obtained from one mole of reactant but the mass of calcium oxide equals the sum of masses of calcium oxide and carbon dioxide.Just like mass, the total energy of the universe is also conversed.