Question

define chemical equation. what is an unbalanced chemical equation called? which law governs the balancing of a chemical equation? state it

Answer 1

Chemical reactions are the processes in which new substances with new properties are formed.The substance which take part in a chemical reaction are called reactants.The new substances produced  are called products.
An unbalanced chemical equation has unequal no. of atoms  in the reactants and  products.
For ex
Mg + O2 ⇒ MgO
Law of conservation of mass governs the balancing of a chemical equation. According to this law matter can neither be created nor destroyed in a chemical reaction. this means that the total mass of all the reactants must be equal to the total mass of the products.

therefore we cannot write the reaction between magnesium and oxygen in such a way
Mg + O2 ⇒ MgO
'
the right way to write it is
2Mg + O2 ⇒ 2MgO

Answer 2

Explanation :

Chemical equation : It is a symbolic representation of chemical reaction in which the reactant species are written on the left side of the reaction and product species are written on the right side of the reaction.

It is represented as,

$2H_2+O_2\rightarrow 2H_2O$

In this balanced chemical reaction, $H_2$ and $O_2$ are the reactants which are present on left side and $H_2O$ is the product which is present on right side.

Unbalanced chemical reaction : It is defined as the number of molecules of atoms present on reactant side are not equal to the number of molecules of atoms present on product side.

For example : $H_2+O_2\rightarrow H_2O$ This reaction is an unbalanced chemical reaction.

Law of conservation of mass : It is defined as the mass of reactant must be equal to the mass of product. Or we can say that, number of molecule of atoms present on reactant side must be equal to the number of molecule of atoms present on product side.

$2H_2+O_2\rightarrow 2H_2O$

This equation is a balanced equation which follow the law of conservation of mass.

$H_2+O_2\rightarrow H_2O$

This equation is an unbalanced equation which does not follow the law of conservation of mass.

So, the law governs the balancing of a chemical equation is the law of conservation of mass.