Master Class 10 Science Chapter 1: Chemical Reactions and Equations - Important Questions & Answers for Board Exams 2025

: Class 10 Science Chapter 1 Important Questions & Answers | Chemical Reactions and Equations | CBSE 2025

Ace your CBSE Class 10 Science board exams with this comprehensive guide to Chapter 1, Chemical Reactions and Equations. Find important questions, detailed answers, and expert tips to score full marks.

Welcome, future toppers! As you gear up for your CBSE Class 10 Science board exams, a strong foundation in each chapter is key. Chapter 1, "Chemical Reactions and Equations," is the starting point of your Chemistry syllabus and is crucial for building a solid understanding of the subject. To help you master this chapter, we have compiled a list of the most important questions and answers that are frequently asked in board exams.

Let's dive in and start your journey to scoring a perfect 100!

Understanding the Basics: What is a Chemical Reaction?

Before we jump into the questions, remember that a chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Key indicators of a chemical reaction include a change in state, a change in color, the evolution of a gas, or a change in temperature.

Important Questions and Answers for Chapter 1: Chemical Reactions and Equations

Here are the must-know questions from this chapter to ensure you are fully prepared for your exams.

1. Why should a magnesium ribbon be cleaned before burning in the air?

A magnesium ribbon should be cleaned before burning because it has a coating of magnesium oxide ( $M g O$ ) on its surface. This layer is formed due to the slow reaction of magnesium with the oxygen present in the air. This protective layer is quite stable and prevents the magnesium from burning. Therefore, it needs to be removed with sandpaper to allow the underlying magnesium to come into direct contact with the air for the combustion reaction to occur.

2. What is a balanced chemical equation? Why is it essential to balance a chemical equation?

A balanced chemical equation is an equation where the number of atoms of each element is equal on both the reactant and the product sides.

It is essential to balance a chemical equation to satisfy the Law of Conservation of Mass. This law states that mass can neither be created nor destroyed in a chemical reaction. Balancing the equation ensures that the total mass of the reactants is equal to the total mass of the products.

3. Write the balanced chemical equations for the following reactions: (a) Hydrogen + Chlorine → Hydrogen chloride (b) Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride (c) Sodium + Water → Sodium hydroxide + Hydrogen

Answers: (a) $H_2 + Cl_2 r i g h t a rro w 2 H Cl$ (b) $3 B a Cl_2 + A l_2 (SO_4)_3 r i g h t a rro w 3 B a SO_4 + 2 A lCl_3$ (c) $2 N a + 2 H_2 O r i g h t a rro w 2 N a O H + H_2$

4. A shiny brown colored element ‘X’ on heating in the air becomes black in color. Name the element ‘X’ and the black colored compound formed.

The shiny brown colored element ‘X’ is Copper (Cu).
When copper is heated in the air, it reacts with oxygen to form copper(II) oxide, which is black in color.
The black colored compound formed is Copper(II) oxide (CuO).

The chemical equation for the reaction is: $2 C u (s) + O_{2} (g) He a t 2 C u O (s)$ (Copper) (Oxygen) (Copper(II) oxide)

5. What is the difference between displacement and double displacement reactions? Write equations for these reactions.

Displacement Reaction	Double Displacement Reaction
In this reaction, a more reactive element displaces a less reactive element from its salt solution.	In this reaction, there is an exchange of ions between the reactants.
Example: $F e (s) + C u SO_4 (a q) r i g h t a rro wF e SO_4 (a q) + C u (s)$ <br> Here, iron (more reactive) displaces copper from its salt solution.	Example: $N a_2 SO_4 (a q) + B a Cl_2 (a q) r i g h t a rro wB a SO_4 (s) + 2 N a Cl (a q)$ <br> Here, sodium and barium ions exchange their places.

6. Explain the following terms with one example each: (a) Corrosion (b) Rancidity

(a) Corrosion: It is the process by which metals are gradually deteriorated or eaten up by the action of air, moisture, or chemicals on their surface. A common example is the rusting of iron, which is the formation of a reddish-brown coating of hydrated ferric oxide ( $F e_2 O_3. x H_2 O$ ) on the surface of iron when exposed to moist air.

(b) Rancidity: This is the process of slow oxidation of oil and fat present in food materials, resulting in a change in their smell and taste, making them unpleasant for consumption. For example, potato chips become stale and give off a foul smell when left exposed to the air for a long time. To prevent this, chip manufacturers flush the bags with an inert gas like nitrogen.

7. What do you mean by a precipitation reaction? Explain by giving examples.

A precipitation reaction is a type of chemical reaction in which two soluble salts in an aqueous solution combine, and one of the products is an insoluble salt called a precipitate. This precipitate separates from the solution.

Example: When a solution of barium chloride ( $B a Cl_2$ ) is mixed with a solution of sodium sulphate ( $N a_2 SO_4$ ), a white precipitate of barium sulphate ( $B a SO_4$ ) is formed immediately. $B a C l_{2} (a q) + N a_{2} S O_{4} (a q) \to B a S O_{4} (s) + 2 N a Cl (a q)$ Here, barium sulphate is the white precipitate.

By thoroughly understanding these questions and their answers, you will have a firm grip on the fundamental concepts of "Chemical Reactions and Equations." Remember to practice balancing equations regularly, as it is a skill that will be useful throughout your study of chemistry.

All the best for your exams!

CBSENOTES

Search This Blog