The physical states of the reactants and products  can be represented by using the symbols (s) for  solids, (l) for liquids, (g) for gases and (aq) for  aqueous solution along with their respective  formulae. The word aqueous is written if the  reactant or product is present as a solution in  water. Precipitate can also be represented by using  an arrow pointing downwards (↓) instead of using  symbol (s). 

In the same way, the gaseous state of an evolved gas can be represented by using an arrow pointing  upward in direction (↑) instead of using symbol  (g). The specific condition of the reaction like  temperature, pressure, catalyst etc. is written above  or below the arrow in the chemical equation.  

 

(a) If the reactant or product is present as a solution of  water, it is represented as:  

(i) (s) 

(ii) (l) 

(iii) (aq) 

(iv) ↓  

Ans. 

Reaction of Silver Nitrate with Sodium Chloride - Teachoo-01.jpg

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So, the correct a nswer is (iii) (aq)  

 

(b) The correct way to represent the evolution of gas,  is to use which of the following symbol:  

(i) ↓ 

(ii) → 

(iii) ↑ 

(iv) (g)  

Ans.  

Reaction of Magnesium with Hydrochloric Acid - Teachoo-01.jpg

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So, the correct a nswer is (iii) ↑

 

(c) Complete the missing variable given as X and Y in  the following reaction:  

2Na (s) + 2H 2 O (l) → 2NaOH (X) + H 2 (Y)  

(i) (aq) and (g) 

(ii) (s) and (g)  

(iii) (g) and (l) 

(iv) (g) and (aq)  

 

Ans. Here,

  • Since Na is reacting with water , the NaOH produced will be in aqueous medium , hence ( aq) symbol will be used.
  • H 2 is a gas which is evolved during the reaction, so we use the symbol (g) for it.

 

So, the correct answer is (i) (aq) and (g)  

 

(d) Which of the following reactions is balanced?  

(i) NaCl + 2H 2 O → 2NaOH + 2Cl 2 + H 2   

(ii) 2NaCl + H 2 O → 2NaOH + 2Cl 2 + H 2   

(iii) 2NaCl + 2H 2 O → 2NaOH + Cl 2 + H 2   

(iv) 2NaCl + 2H 2 O → NaOH + Cl 2 + H 2   

 

Ans. 

 

Explanation:

A balanced chemical equation is one in which the number of atoms of both reactants and products are equal. 

 

In reaction I:

 

 

Na

H

O

Cl

Reactant

1

4

2

1

Product

2

4

2

4

 

Since the number of Na and Cl atoms in reactant and product is not equal, it is not a balanced equation.

 

In reaction II:

 

 

Na

H

O

Cl

Reactant

2

2

1

2

Product

2

4

2

4

 

Since the number of H, O and Cl atoms in reactant and product is not equal. It is not a balanced equation. 

 

In reaction III:

 

 

Na

H

O

Cl

Reactant

2

4

2

2

Product

2

4

2

2

 

Since the number of all atoms in reactants and products is equal, it is a balanced equation.

 

In Reaction IV:

 

 

Na

H

O

Cl

Reactant

2

4

2

2

Product

1

3

1

2

 

Since the number of Na, H, and O atoms is not equal in reactant and product, it is not a balanced equation.


So, the correct answer is  (iii) 2NaCl + 2H 2 O → 2NaOH + Cl 2 + H 2

 

(e) Which of the following reactions is correct?  

(i) Mg (aq) + H 2 SO 4 (aq) → MgSO 4 (aq) + H 2 ↑  

(ii) Mg (s) + H 2 SO 4 (aq) → MgSO 4 (aq) + H 2 ↑  

(iii) Mg (s) + H 2 SO 4 (l) → MgSO 4 (l) + H 2 (g)  

(iv) Mg (s) + H 2 SO 4 (l) → MgSO 4 (s) + H 2   

 

Ans. (ii) Mg (s) + H 2 SO 4 (aq) → MgSO 4 (aq) + H 2

Explanation:

A balanced chemical equation is one in which the number of atoms of both reactants and products are equal. 

 

In reaction I:

 

Mg

H

O

S

Reactant

1

2

2

1

Product

1

2

 

4




In reaction II:

 

 

Mg

H

O

S

Reactant

1

2

4

1

Product

1

2

4

1


Since the number of all atoms in reactants and products is equal, it is a balanced equation.

 

In reaction III:

 

 

Mg

H

O

S

Reactant

       

Product

       




In Reaction IV:

 

 

Mg

H

O

S

Reactant

       

Product

       

 

  1. Class 10
  2. Chapter 1 Class 10 - Chemical Reactions and Equations (Term 1)

About the Author

CA Maninder Singh's photo - Founder at Teachoo
CA Maninder Singh
CA Maninder Singh is a Chartered Accountant for the past 11 years and a teacher from the past 11 years. He teaches Science, Accounts and English at Teachoo