Question

Define the law of conservation of mass.

Answer 1

Hint: The law of conservation talks about the dependence of the products on the reactants in terms of their mass. The law of conservation of mass is used to predict the mass of products formed based on the mass of reactants used for the reaction.

Complete step by step answer:

The law of conservation of mass states that mass in an isolated system is neither created nor destroyed by chemical reactions or physical transformations but it can be transformed from one to another.

According to the law of conservation of mass, the sum of mass of reactants as well as products are equal in a chemical reaction.

The law of conservation of mass is useful in calculating unknown masses, such as the amount of gas consumed or produced during a reaction.

The law of conservation of mass was given by Antoine Lavoisier in 1789.

The concept of mass conservation is widely used in chemistry, mechanics as well as in fluid dynamics.

Let us write a few reactions and find the mass of products formed using the law of conservation of mass.

$\text{2}{{\text{H}}_{2}}\text{ + }{{\text{O}}_{2}}\text{ }\to \text{ 2}{{\text{H}}_{2}}\text{O}$

Let us take the mass of hydrogen as 4g and mass of oxygen as 32. By the law of conservation of mass, the mass of water formed should be 36g.

 We will find the mass of water formed by applying the mole concept.

Since 2 moles of hydrogen molecules and 1 mole of oxygen molecules react, the number of moles of water molecules formed is 2.

The mass of 1 mole of water molecule is 18g, hence 2 moles of water molecules will weigh 36g.

We see that the law of conservation of mass holds good for the above reaction.

Note: The law of conservation of mass holds good for chemical reactions as long as the energy is not lost in the reaction. In terms of physics, law of conservation of mass holds good as long the frame of reference is inertial. This is because we cannot define all the energies in a non-inertial frame.