Question

How do you use the law of conservation of mass to explain why a chemical equation must be balanced?

Answer 1

Hint: To solve the question, we have to know the law of conservation of mass which states that in a reaction mass can neither be created nor be destroyed, it can only be transferred or exchanged i.e. the mass is conserved in the reaction.

Complete answer:
So in the question it is asked how we can use the law of conservation of mass to explain about why a chemical equation should be balanced.
From the lower classes we are studying about various reactions taking place. And from the time we start dealing with the chemical reactions, we are introduced with the concept of representing chemical reactions as chemical equations.
We are familiar that all elements have their own chemical representation. We generally represent the first letter of the name of the element in Latin or Greek language or we use two letters associated with the name of the element. First letter will always be in capital letters and the second alphabet in small letters.
So with the aid of these chemical symbols we easily represent each compound and write the chemical equation for the reaction taking place.
As we all know the chemical equation will have two sides: a reactant side in the left hand side where we represent the reactants involved and the right hand side consists of the products formed and hence called as the product.
In between the reactant side and product side an arrow is present, pointing towards the product side which symbolizes the reactants on reaction gives the product.
Now let us discuss conservation of mass, so the law states that in a reaction mass can neither be created nor be destroyed, it can only be transferred or exchanged i.e. the mass is conserved in the reaction.
So according to, law of conservation of mass, the mass of products formed should be equal to the mass of the reactants involved in the reaction. The mass is only exchanged from reactant side to product side.
To get a better understanding let us consider the chemical equation as mathematical calculation.
We will only write as $2+2=4$ not $2+2=3$
The terms on the left side represent the reactant side and the equal sign represents the forward arrow and left side will represent the product side.
So the number of atoms in the reactant side should be equal to the number of atoms in the product side.
Example: ${{H}_{2}}+{{O}_{2}}\to {{H}_{2}}O$, the given equation is not balance since the number of oxygen atom differs on both sides. The equation should be balanced to satisfy the law of conservation of mass.
Hence the balanced chemical equation is as follows:
$2{{H}_{2}}+{{O}_{2}}\to 2{{H}_{2}}O$

Note:
The number we give to balance the equation is called as the coefficients. While balancing a chemical equation caution should be taken when the polyatomic species are involved. And we should not change the subscripts associated with the atoms since if we change the subscripts it will change the stoichiometric ratio of the compound.