WBBSE Solutions For Class 8 School Science Chapter 2 Element Compound And Chemical Reaction Very Short Answer Type Questions

Chapter 2 Element Compound And Chemical Reaction VSAQs

Question 1. In photosynthesis, which form of energy is converted into chemical energy?
Answer:

In photosynthesis, light energy is converted into chemical energy.

Question 2. What is required to initiate a chemical reaction?
Answer:

Energy is required to initiate a chemical reaction.

Question 3. Mention a reaction which is induced/initiated by light.
Answer:

Photosynthesis is a reaction which is induced/initiated by light. Here, green plants can utilize solar energy (in the form of visible light) to produce glucose from carbon dioxide and water. The process can be represented in a simplified way as follows:

⇒ \(6 \mathrm{CO}_2+6 \mathrm{H}_2 \mathrm{O} \stackrel{\text { light }}{\longrightarrow} \mathrm{C}_6 \mathrm{H}_{12} \mathrm{O}_6+6 \mathrm{H}_2 \mathrm{O}\)

Question 4. Give one example, where a chemical reaction is initiated by applying pressure.
Answer:

In crackers, a mixture of potassium chlorate and sulphur explodes when pressure is applied to them, Give one example, where a chemical reaction is initiated by electricity.

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Question 5. Give one example, where a chemical reaction is initiated by electricity.
Answer:

When an electric spark is passed through a mixture of hydrogen and oxygen gas, water will be formed. If no current is passed through it, no chemical change will take place.

⇒ \(2 \mathrm{H}_2+\mathrm{O}_2 \rightarrow 2 \mathrm{H}_2 \mathrm{O}\)

Question 6. What do you mean by a catalyst?
Answer:

Catalyst:

A substance which can alter the rate of a chemical reaction without undergoing any net change in its chemical composition at the end of the chemical reaction is called a catalyst.

Question 7. Write the name and formula of baking soda. Baking soda is sodium bicarbonate.
Answer:

Its formula is NaHCO₃.

Question 8. Give an example of a catalyzed reaction. During the preparation of ammonia (NH₃) from nitrogen and hydrogen gas, finely divided iron powder is used as a catalyst. So this is an example of a catalyzed reaction.
Answer:

⇒ \(\mathrm{N}_2+3 \mathrm{H}_2 \rightarrow 2 \mathrm{NH}_3 (Finely divided iron powder used as catalyst)\)

Question 9. What catalyst is used during the industrial process of manufacture of sulphuric acid?
Answer:

Industrially sulphuric acid is prepared by the reaction of sulphur dioxide and oxygen in the presence of a vanadium pentoxide (V₂O₅) catalyst.

⇒ \(2 \mathrm{SO}_2+\mathrm{O}_2 \rightarrow 2 \mathrm{SO}_3
\left\{\right. catalyst: Vanadium pentoxide \left.\left(\mathrm{V}_2 \mathrm{O}_5\right)\right\}\)

Question 10. Give an example of an enzyme-catalyzed reaction.
Answer:

Example Of An Enzyme-Catalyzed Reaction:

Urease is an enzyme. It catalyzes the hydrolysis of urea into ammonia and carbon dioxide.

⇒ \(\mathrm{NH}_2 \mathrm{CONH}_2+\mathrm{H}_2 \mathrm{O} \rightarrow 2 \mathrm{NH}_3+2 \mathrm{CO}_2\)

Question 11. Write the name of an enzyme which is found in our stomach.
Answer:

Pepsin is an enzyme which is found in our stomach.

Question 12. What do you mean by an exothermic reaction?
Answer:

Exothermic Reaction: Chemical reactions which proceed with the evolution of heat energy are called exothermic reactions.

Question 13. What do you mean by an endothermic reaction?
Answer:

Endothermic Reaction: Chemical reactions which proceed with the absorption of heat energy are called endothermic reactions.

Question 14. Give an example of an exothermic reaction.
Answer:

Example Of An Exothermic Reaction:

The combustion of methane is an example of an exothermic reaction.

⇒ \(\mathrm{CH}_4+2 \mathrm{O}_2 \rightarrow \mathrm{CO}_2+2 \mathrm{H}_2 \mathrm{O}+\text { heat }(\mathrm{Q})\)

Question 15. Give an example of an endothermic reaction.
Answer:

Example Of An Endothermic Reaction:

Passage of steam over heated coke produces carbon monoxide and hydrogen. Heat is absorbed during the process. This is an endothermic reaction.

⇒ \(\mathrm{C}+\mathrm{H}_2 \mathrm{O} \rightarrow \mathrm{CO}+\mathrm{H}_2-\text { heat }(\mathrm{Q})\)

Question 16. When ammonium chloride is dissolved in water in a test tube, what type of change is occurred?
Answer:

When ammonium chloride is dissolved in water, heat is absorbed and as a result, droplets of water condense in the outer surface of the test tube which becomes cold. But this is a physical change and not a chemical change.

Question 17. Name a gas which is used in welding.
Answer:

Acetylene (C₂H₂) is used for welding.

Question 18. Name one gaseous oxidizing agent and one gaseous reducing agent.
Answer:

Oxygen is an oxidizing agent and hydrogen is a reducing agent.

Question 19. Name the oxidant and reductant in the reaction Fe + Cu²⁺ = Fe²⁺ + Cu.
Answer:

⇒ \(\mathrm{Fe}-2 \mathrm{e} \rightarrow \mathrm{Fe}^{2+}:\)This is oxidation and Fe is the reductant

⇒ \(\mathrm{Cu}^{2+}+2 \mathrm{e} \rightarrow \mathrm{Cu}:\)This is the reduction and Cu²⁺ is the oxidant

Question 20. Name an enzyme that can decompose peroxide compounds.
Answer:

Catalase enzyme.

Question 21. \(\mathrm{Sn}^{2+} \rightarrow \mathrm{Sn}^{4+}+2 \mathrm{e} \rightarrow\) Is this oxidation or reduction reaction?
Answer:

Since the loss of electron means oxidation hence \(\mathrm{Sn}^{2+} \rightarrow \mathrm{Sn}^{4+}+2 \mathrm{e} \rightarrow\) is an oxidation reaction. Sn²⁺ is the reducing agent.

Question 22. What do you mean by rancidity?
Answer:

Rancidity:

The condition produced by aerial oxidation of fats and oils in food marked by unpleasant smell and taste is called rancidity.

Question 23. Name 1. a reducing agent that contains oxygen and 2. an oxidizing agent that does not contain oxygen.
Answer:

1. Sulphur dioxide (SO₂ )
2. Ferric chloride (FeCl₃)

Question 24. What is autocatalysis?
Answer:

Autocatalysis:

In certain reactions, one of the products acts as a catalyst. This phenomenon is known as autocatalysis.

Acetic acid (CH₃COOH) and ethyl alcohol (C₂H₅OH) are produced in the hydrolysis of ethyl acetate (CH₃COOC₂H₅). This reaction is initially very slow but acetic acid acts as an auto-catalyst in the reaction and gradually increases the rate of the reaction.

⇒ \(\mathrm{CH}_3 \mathrm{COOC}_2 \mathrm{H}_5+\mathrm{H}_2 \mathrm{O} \rightarrow \mathrm{CH}_3 \mathrm{COOH}+\mathrm{C}_2 \mathrm{H}_5 \mathrm{OH} .\)

Question 25. Give an example of exothermic physical change.
Answer:

Example Of Exothermic Physical Change:

When some concentrated sulphuric acid is added to water taken in a beaker, the acid dissolves with the evolution of heat. This is an example of exothermic physical change.

Question 26. Mention two simple household methods to prevent the rancidity of food.
Answer:

The development of rancidity of food can be prevented by:

1. keeping food in a refrigerator
2. storing food away from light