RBSE Class 8 Science Chapter 4 Chemical Reactions Textbook Solutions

RBSE Class 8 Science Chapter 4 Chemical Reactions solutions is one of the best resources for students to revise all the important concepts of the chapter and score good marks. These solutions will help build a strong foundation for students to understand all the key concepts of this chapter and master it. All the questions and important topics of the RBSE Class 8 Science Solutions for Chapter 4 have been extensively covered and made it simpler for students to understand easily.

Students can find chapter-wise explanations of important questions of RBSE Class 8 Science, and we hope this will definitely help them to prepare for the RBSE Class 8 2020 exam with ease. Besides, students need to implement a strategic learning process to score well in the examinations. Here, we bring you a collection of the Important Topics and Questions for all the chapters of RBSE Class 8 Science.

Meanwhile, here we have covered the important topics and questions with solutions for Chapter 4 from the RBSE Class 8 Science Syllabus. We hope by practising these questions, students will be able to get an in-depth understanding of the chapter and revise it thoroughly before their exams. This will create a strong foundation for students and prepare them for higher classes and score good grades in the exams.

Rajasthan Board Class 8 Science Chapter 4: BYJU’S Important Questions & Answers

RBSE Class 8 Science Chapter 4 Objective Questions: Textbook Important Questions and Solutions

Choose the correct options for the following:

Question 1: The following is an example of which type of reaction?

NH₃ (g) + HCl (g) → NH₄Cl (s)

1. Addition
2. Displacement
3. Decomposition
4. Neutralisation

Answer: a) Addition

Question 2: In oxidation reaction,

1. Oxygen is added
2. Hydrogen is added
3. Oxygen is removed
4. Hydrogen is removed

Answer: a) Oxygen is added

Question 3: Acid changes blue litmus to

1. White
2. Red
3. Black
4. Purple

Answer: b) Red

Question 4: Copper (Cu) + Oxygen (O₂) →

1. H₂O
2. O₂
3. CuO
4. CuSO₄

Answer: c) CuO

Fill in the blanks:

Question 5: Disassociation is the opposite of ______________________ reaction.

Answer: Addition

Question 6: On adding fixed volume of acid and bases _____________ and _____________ are obtained.

Answer: Salt and water

Question 7: Addition of oxygen is known as ______________________ .

Answer: Oxidation

Question 8: The reaction in which energy is liberated is called ______________ .

Answer: An exothermic reaction

Match the following columns:

Answers:

RBSE Class 8 Science Chapter 4 Short Answer Type Questions: Textbook Important Questions and Solutions

Question 1: Write an example of displacement reaction.

Answer: The process of reaction in which a more reactive compound displaces a less reactive compound is known as displacement reaction.

Question 2: Why does lime water turn milky when carbon dioxide gas passes through it?

Answer: Calcium hydroxide is said to be soluble in water which produces an alkaline solution known as lime water. Lime is primarily composed of calcium carbonate. When carbon dioxide gas passes through lime water, it turns milky due to the formation of calcium carbonate.

Here’s the chemical reaction:

Calcium carbonate (CaCO₃) —————> Calcium Oxide (CaO) + Carbon dioxide (CO₂)

(On heating)

Question 3: Explain addition reaction with example.

Answer: When two or more elements or compounds react with each other to form a product, that process is known as addition reaction. For example, when we take some iron dust in an ignition spoon and heat it till it’s red hot. Now we insert the spoon in a gas jar that’s filled with oxygen, we can see that the iron dust burns in flames resulting in the formation of ferric oxide.

Fe (Iron powder) + O₂ (Oxygen) → Fe₃O₄ (Ferric oxide)

Question 4: Explain displacement reaction with example.

Answer: The reaction process in which a more reactive compound displaces with a less reactive compound is known as a displacement reaction. For example, you can make a solution of copper sulphate in a test tube by adding a non rusted iron nail in it and then leave it for some time. We will gradually notice there is a deposit of light brown colour on the iron nail. This layer is of copper metal. In due course, the solution colour changes from blue to green as the copper from the copper sulphate gets deposited on the iron nail. Hence, proved that a more reactive metal displaces a less reactive metal. Iron (Fe) is more reactive than Copper (Cu) and hence displaces Copper (Cu) and forms Iron Sulphate (FeSO₄).

Fe (Iron) + CuSO₄ (Copper Sulphate) → FeSO₄ (Ferrous Sulphate) + Cu (Copper)

Question 5: Write properties of Chemical Reaction.

Answer: Given below are the specific properties of Chemical Reactions:

1. Production of Gas: When fuels such as diesel, petrol, kerosene, etc. burn and react with air, they form carbon dioxide gas. Similarly, when we burn carbon with oxygen, it produces carbon dioxide.C (Carbon) + O₂ (Oxygen) → CO₂ (Carbon dioxide)
2. Change in colour: When we cut an apple into two halves, we’ll notice that after some time the colour changes to brown due to the presence of iron in the apple. This reacts with oxygen present in the air and forms iron oxide.
3. Change in heat: When we add ammonium chloride in water, it becomes cold in the process.
4. Precipitation: A bar of soap precipitates in salty water, but it forms a rich foam of froth in freshwater.

RBSE Class 8 Science Chapter 4 Long Answer Type Questions: Textbook Important Questions and Solutions

Question 6: How many types of chemical reactions are there? Explain any four with examples.

Answer: There are 6 types of chemical reactions which are given below:

1. Addition reaction
2. Dissociation or Decomposition reaction
3. Displacement reaction
4. Oxidation reaction and Reduction reaction
5. Neutralization reaction
6. Endothermic and Exothermic reaction

Given below is the explanation of four reactions with examples:

1. Addition reaction: The process in which two or more elements or compounds combine with each other to form a new product or compound. This reaction is also called a combination reaction. For example, when magnesium reacts with oxygen, it forms a combination of magnesium oxide:2Mg(s) + O₂(g) → 2MgO(s)
2. Dissociation reaction: The reaction process in which a reactant breaks down in two or more products or compounds is called a dissociation reaction. This reaction is also known as decomposition reaction. For example, when we heat calcium carbonate, it starts liberating a gas. Now when we insert it in lime water, the mixture gets milky white when exposed to gas and results in the formation of carbon dioxide. When calcium carbonate is heated, it forms calcium oxide and carbon dioxide:Calcium carbonate (CaCO₃)—→ Calcium oxide (CaO) + Carbon dioxide (CO₂)(On heating)
3. Neutralization reaction: The reaction process in which an acid and a base react together to form salt and water is known as neutralization reaction. For example, when Hydrochloric acid (HCl) reacts with Sodium hydroxide (NaOH) as base, it results in the formation of Sodium Chloride (NaCl), i.e salt and water (H₂O):HCl + NaOH → NaCl + H₂O + Energy
4. Endothermic and Exothermic reaction: In simple terms, the endothermic reactions tend to absorb energy from the environment in the form of heat. While, the exothermic reaction tends to release energy into the environment from the system. For example, when we take a jar filled with water and add some potassium nitrate powder in it, we notice a change in temperature. The decrease in temperature is due to the absorption of heat which is known as endothermic reaction. On the other hand, if we repeat the above experiment with sodium hydroxide, we’ll notice a rise in temperature due to liberation of energy which is known as exothermic reaction.

Question 7: Give example with experiment any two properties of chemical reaction.

Answer: Here are two properties of a chemical reaction:

1. 1. Production of gas: In a chemical reaction, if one of the reactants is in a liquid state or solution form, it results in the formation of a gas. For example, when we take a few zinc granules in a test tube and add dilute sulphuric acid to it. We would notice a gas is liberated which burns with explosion when a burning matchstick comes in contact with the mouth of the test tube. This gas is hydrogen.

1. Change in colour: When we cut an apple into two half pieces and exposed to air, the colour of the apple changes to brown. This is due to the presence of iron in the apple, which reacts with oxygen present in the environment and results in the formation of iron oxide.

Question 8: Explain with example:

1. Neutralization reaction
2. Dissociation reaction
3. Exothermic reaction
4. Endothermic reaction

Answer:

1. Neutralization reaction: The reaction process in which an acidic oxide reacts with basic oxide and forms salt and water is known as Neutralization reaction. For example, HCl (Hydrochloric acid) + NaOH (Sodium hydroxide) → NaCl + H₂O (Sodium Chloride)
2. Dissociation / Decomposition reaction: The process in which a reactant breaks down in two or more simpler products or compounds is called a dissociation or decomposition reaction. For example, when we heat calcium carbonate, it forms calcium oxide and carbon dioxide:Calcium carbonate (CaCO₃)—→ Calcium oxide (CaO) + Carbon dioxide (CO₂)(On heating)
3. Exothermic reaction: Reactions which are accompanied with the liberation of heat are known as exothermic reactions. For example, when carbon burns in oxygen, it releases carbon dioxide gas and heat:C (Carbon) + Oxygen (O₂) → Carbon dioxide (CO₂) + Heat
4. Endothermic reaction: Reactions which are accompanied with the absorption of heat are known as endothermic reactions. For example, when carbon and sulphur are heated together, they react together to form carbon disulphide as heat is absorbed in the process:C (Carbon) + Sulphide (2S) → Carbon disulphide (CS₂) – Heat

RBSE Class 8 Science Chapter 4 Additional Questions and Solutions

Multiple Choice Questions (MCQs)

Choose the correct options for the following:

Question 1: What is the chemical reaction in which heat is released called?

1. Exothermic reaction
2. Endothermic reaction
3. Neutralization reaction
4. Dissociation reaction

Answer: a) Exothermic reaction

Question 2: _____________________ is the change in any substance due to chemical activity.

1. Physical reaction
2. Mixed reaction
3. Chemical reaction
4. Biological reaction

Answer: c) Chemical reaction

Question 3: What is the reaction in which a reactant breaks down to form two or more products or compounds?

1. Addition reaction
2. Decomposition reaction
3. Neutralization reaction
4. Exothermic reaction

Answer: b) Decomposition reaction

Question 4: The reaction in which energy is absorbed is known as _________________ reaction.

1. Neutralization reaction
2. Dissociation reaction
3. Endothermic reaction
4. Exothermic reaction

Answer: c) Endothermic reaction

Question 5: What does an oxidation reaction involve?

1. Absorption of oxygen only
2. Consumption of oxygen and release of hydrogen
3. Liberation of oxygen and consumption of hydrogen
4. Absorption of hydrogen only

Answer: b) Consumption of oxygen and release of hydrogen

Question 6: How many elements react to form new compounds in an addition reaction?

1. One only
2. Two only
3. Two or more
4. None

Answer: c) Two or more

Question 7: What is a reduction reaction?

1. When oxygen combines with a substance
2. When oxygen reduces from a substance
3. When hydrogen reduces from a substance
4. None of the above

Answer: b) When oxygen reduces from a substance

Question 8: What are the substances which react together called?

1. Mixtures
2. Reactants
3. Combinations
4. None of the above

Answer: b) Reactants

Question 9: Substances formed through a chemical reaction are known as _____________.

1. Molecules
2. Bonds
3. Compounds
4. Products

Answer: d) Products

Question 10: When fuels such as diesel, petrol, etc. burn, they react with _____________ to form CO₂ gas.

1. Acid
2. Air
3. Water
4. Gas

Answer: b) Air

Question 11: A chemical combination involves combining of:

1. Same type of elements
2. Same type of compounds
3. Two or more atoms
4. Any two or more elements or compounds

Answer: d) Any two or more elements or compounds

Question 12: How many products are formed in a combination reaction?

1. One only
2. Two only
3. One or two only
4. No specific number

Answer: a) One only

Question 13: What is being oxidised in a reaction between zinc and iodine resulting in the formation of zinc iodide?

1. Zinc atom
2. Zinc ions
3. Iodine
4. Iodide ions

Answer: a) Zinc atom

Question 14: Soap ___________________ in salty water due to its hardness.

1. Condenses
2. Evaporates
3. Precipitates
4. Deposits

Answer: c) Precipitates

Question 15: Dissociation reaction is also known as __________________ reaction.

1. Addition
2. Decomposition
3. Displacement
4. Oxidation

Answer: b) Decomposition

Question 16: _____________ and ______________ reactions are opposites of each other and take place simultaneously.

1. Addition and dissociation
2. Oxidation and reduction
3. Displacement and neutralization
4. Endothermic and exothermic

Answer: b) Oxidation and reduction

Question 17: Calcium carbonate (CaCO₃) → Calcium Oxide (CaO) + Carbon dioxide (CO₂) is an example of:

1. Addition reaction
2. Neutralization reaction
3. Decomposition reaction
4. Oxidation reaction

Answer: c) Decomposition reaction

Question 18: When Copper (Cu) reacts with Oxygen (O₂), it forms ___________________.

1. Copper sulphide (CU₂S)
2. Copper oxide (CuO)
3. Carbon dioxide (CO₂)
4. Hydrogen (H₂)

Answer: b) Copper oxide (CuO)

Question 19: In a reduction reaction, when hydrogen gas reacts with hot copper oxide, then it forms copper and water due to the liberation of _____________.

1. Hydrogen
2. Nitrogen
3. Oxygen
4. Carbon dioxide

Answer: c) Oxygen

Question 20: In an addition reaction, iron dust burns with oxygen to form ______________ oxide.

1. Copper
2. Lead
3. Ferric
4. Calcium

Answer: c) Ferric

Question 21: Rusting of iron happens in the presence of __________ and water.

1. Oxygen
2. Hydrogen
3. Carbon dioxide
4. Nitrogen

Answer: a) Oxygen

Short Answer Questions:

Question 1: What are reactants and products?

Answer: Substances which react together in a chemical reaction are known as reactants, while those substances which are formed through their reaction are known as products.

Question 2: How do we write a chemical reaction?

Answer: While writing a chemical reaction we write reactants on the left of arrow (–>) and products are written on the right side.

Question 3: What happens when we leave an iron pan in the open environment?

Answer: When left in the open and humid environment, there is a chemical reaction in which the iron of the pan reacts with oxygen in the presence of water and results in the formation of iron oxide (rust).

Question 4: What happens when we burn coal in the presence of oxygen?

Answer: When coal is burnt in the presence of oxygen, it generates carbon dioxide and heat in the combustion process.

Question 5: Explain why an half cut apple changes into a brown colour in the open environment.

Answer: When an apple is cut into two halves, it changes into a brown colour due to the presence of iron in the apple which reacts with oxygen present in the environment that results in the formation of iron oxide.

Question 6: What happens when we add ammonium chloride in water?

Answer: When we add ammonium chloride in water, it cools down the chemical reaction.

Question 7: What is a redox reaction?

Answer: The chemical reaction in which oxidation and reduction reactions take place simultaneously is known as a redox reaction or oxy-reduction reaction.

Question 8: What is an oxidizing agent with examples?

Answer: A substance that oxidizes with other substances by reducing hydrogen and providing oxygen is known as an oxidizing agent. An oxidizing agent or oxidant gains electrons in a chemical reaction. Examples of oxidizing agents include halogens, nitric acid, etc.

Question 9: Define a catalyst.

Answer: A catalyst is a substance which accelerates the rate of a chemical reaction without undergoing any chemical change itself.

We hope that the above mentioned solutions of “RBSE Class 8 Science Chapter 4 Chemical Reactions” will help students build a strong foundation of the different concepts mentioned in the chapter.