10th Class Science Chemical Reactions and Equations Balancing of Chemical Equations

       Balancing of Chemical Equations

The chemical equations must be written in accordance with the law of conservation of mass. The law of conservation of mass states that:

"The matter can neither be created nor destroyed".

OR

"In a chemical reaction, the total mass of reactants is equal to the total mass of products".                   

We always have to represent a chemical reaction by balancing the equation.

"A balanced chemical equation is the one in which the atoms of each element must be equal on both sides of the equation".

\[{{N}_{2}}+3{{H}_{2}}\to 2N{{H}_{3}}\]

In the above equation we see that the number of atoms of each elements is same on both side of the reaction and hence it can be said as balanced. To make the atoms of each element equal on both sides of the equation is called balancing of chemical equation.                             

Steps to be followed for balancing chemical equation

• Write word equation for the reaction with reactants on L.H.S. and products on R.H.S. separated by an arrow head. e.g. Aluminium + Hydrochloric acid \[\to \] Aluminium chloride + hydrogen.
• Convert the word equation into symbols/formula of the compounds. e.g. above equation can be written as

\[Al+HCl\to AlC{{l}_{3}}+{{H}_{2}}\]

• Equate the number of each type of atoms on both side of the reaction one by one.

\[2Al+6HCl\to 2AlC{{l}_{3}}+3{{H}_{2}}\]

Finally count the number of atoms of each element on reactant and product sides and if they are equal then the equation is balanced.

        What will happen when a piece of iron metal is placed is copper sulphate solution?

(a) Physical change

(b) A chemical reaction

(c) Evolution of gas

(d) Heat will be evolved.

(e) None of these

Answer: (b)

       Respiration is an example of chemical change. The reactants involved in this are:

(a) Carbon dioxide

(b) Carbon dioxide + water

(c) Glucose

(d) Glucose and oxygen

(e) None of these

Answer: (d)

Explanation

Glucose and Oxygen as the reaction is:

\[{{C}_{6}}{{H}_{12}}{{O}_{6}}+6{{O}_{2}}-6C{{O}_{2}}+6{{H}_{2}}O+\] Energy glucose.

       A balanced chemical equation is in accordance with which one of the following laws given Below?

(a) Law of conservation of energy

(b) Law of conservation of mass

(c) Law of constant proportion

(d) Law of multiple proportion

(e) None of these

Answer: (b)

Explanation 

Law of conservation of mass as the total mass of reactant in always equal to the total mass of products.

         Which among the following is a balanced chemical equation?

(a) \[Mn{{O}_{2}}+4HCl\to MnC{{l}_{2}}+C{{l}_{2}}+2{{H}_{2}}O\]

(b) \[Fe+{{H}_{2}}O\to F{{e}_{3}}{{O}_{4}}+{{H}_{2}}\] 

(c) \[Zn+HCl\to ZnC{{l}_{2}}+{{H}_{2}}\]

(d) \[2KCl{{O}_{3}}\to 2KCl+{{H}_{2}}\]

(e) None of these

Answer: (a)

Explanation 

\[Mn{{O}_{2}}+4HCl\to MnC{{l}_{2}}+C{{l}_{2}}+2{{H}_{2}}O\] as the atoms of all elements are equal on both sides of the reaction.

       What is the corresponding change in colour when iron nail is dipped in the blue copper sulphate solution?

(a) Red

(b) White

(c) Green

(d) Black

(e) None of these

Answer: (C)