1 . Chemical Reactions and Equations

CBSE Class 10 Science Chapter 1. Chemical Reactions and Equations

Chapter 01 : Chemical Reactions and Equations

Class 10 Science Chapter 1 Chemical Reactions and Equations Multiple Choice Questions , 2 Marks Questions, 3 Marks Questions and Answers :

CBSE Previous Years Questions and Answers for 2008

Question: Balance the following chemical equations : [2008 1M]

Solution: The balance chemical equation is:

Question: Why is respiration considered an exothermic process ? [1M]

Answer : Respiration is exothermic because it involves the breakdown of carbohydrates to form glucose, which then reacts with oxygen in cells, releasing a large amount of heat energy as a byproduct.

Question: Given an example of a decomposition reaction . Describe an activity to illustrate such a reaction by heating . [2M]

Answer : One example of a decomposition reaction is :

Take about 2 grams of ferrous sulphate crystals and place them in a dry boiling tube. Set up the boiling tube over the flame of a burner or spirit lamp. Observe the changes that occur as the ferrous sulphate crystals are heated. Then, observe the color changes and the release of gas.

The chemical reaction is :

CBSE Previous Years Questions and Answers for 2009

Question: Balance the following chemical equation is :

Answer : The balance chemical equation is :

Question: (i) What is the colour of ferrous sulphate crystals ? How does this colour change after heating ?

(ii) Name the products formed on strongly heating ferrous sulphate crystals . What type of chemical reaction occurs in this change ?

Answer : (i) The ferrous sulphate crystals is green colour . When ferrous sulphate crystals are heated, the colour changes from green to white due to the formation of ferric oxide (Fe₂O₃) during the decomposition reaction.

(ii) On strongly heating ferrous sulphate crystals, the products formed are ferric oxide (Fe₂O₃), sulphur dioxide (SO₂), and sulphur trioxide (SO₃).

The chemical reaction that occurs is a decomposition reaction.

The reaction chemical reaction :

CBSE Previous Years Questions and Answers for 2010

Question: What change in the colour of iron nails and copper sulphate solution you observe after keeping the iron nails dipped in copper sulphate solution for about 30 minutes ? [1M]

Answer : The colour of iron nails changes to brownish due to the deposition of copper on the nails. The blue colour of copper sulphate solution fades as copper ions transfer to the iron nails.

Question: What happen when an aqueous solution of sodium sulphate reacts with an aqueous solution of barium chloride ? State the physical conditions of reactants in which the reaction between them will not take place . Write the balanced chemical equation for the reaction and name the type of reaction. [2M]

Answer : When an aqueous solution of sodium sulphate reacts with an aqueous solution of barium chloride, a white precipitate of barium sulphate forms, while sodium chloride remains in solution.

The physical conditions in which the reaction between sodium sulphate and barium chloride will not take place are when either reactant is absent in aqueous solution, or if the reactants are not dissolved in water.

The balanced chemical equation for the reaction is:

This reaction is a double displacement reaction or precipitation reaction.

CBSE Previous Years Questions and Answers for 2018

Question: Decomposition reactions require energy either in the form of heat or light or electricity for breaking down the reactions . Write one equation each for decomposition reactions where energy is supplied in the form of heat, light and electricity .

Answer : The examples of decomposition reactions where energy is supplied in the form of heat, light, and electricity:

Decomposition with Heat:

Calcium carbonate ( ) decomposes into calcium oxide (CaO) and carbon dioxide () when heat is supplied.

Decomposition with Light:

Silver chloride (AgCl) decomposes into silver (Ag) and chlorine gas () when exposed to light.

Decomposition with Electricity:

Water () decomposes into hydrogen gas () and oxygen gas () when electricity is passed through it.

CBSE Previous Years Questions and Answers for 2019

Question : 2 g of silver chloride is taken in a china dish and the china dish is placed in sunlight for sometime. What will be your observation in this case ? write the chemical reaction involved in the form of a balanced chemical equation . Identify the type of chemical reaction .

Answer : When 2 grams of silver chloride (AgCl ) is exposed to sunlight, it undergoes a photochemical decomposition reaction. The observation in this case would be a change in the color of the silver chloride from white to gray, indicating the formation of elemental silver. The balanced chemical equation for the reaction is:

This reaction involves the breakdown of silver chloride into silver (Ag) and chlorine gas () under the influence of sunlight. It is a photochemical decomposition reaction, as it is triggered by the absorption of light energy.

Question : Identify the type of reaction taking place in each of the following cases and write the balanced chemical equation for the reactions .

(i) Zinc reacts with silver nitrate to produce zinc nitrate and solver .

(ii) Potassium iodine reacts with lead nitrate to produce potassium nitrate and lead iodide .

Answer : (i) The type of reaction taking place in the first case is a single displacement reaction or a single replacement reaction. The zinc displaces silver from silver nitrate to form zinc nitrate and silver.

The balanced chemical equation for the reaction is :

(ii) The type of reaction taking place in the second case is a double displacement reaction or a double replacement reaction. Potassium iodide reacts with lead nitrate to produce potassium nitrate and lead iodide.

The balanced chemical equation for the reaction is:

CBSE Previous Years Questions and Answers for 2020

Question : Calcium oxide reacts vigorously with water to produce slaked lime .

This reaction can be classified as:

(A) Combination reaction (B) Exothermic reaction

Which of the following is a correct option? [2020 1M]

Answer : (B) Exothermic reaction .

Question : When hydrogen sulphide gas is passed through a blue solution of copper sulphate, a black precipitate of copper sulphide is obtained and the sulphuric acid so formed remains in the solution. The reaction is an example of a: [1M 2020]

(a) Combination reaction (b) Displacement reaction

Answer : (d) Double displacement reaction

[The chemical reaction is : ]

Question : In a double displacement reaction such as the reaction between sodium sulphate solution and barium chloride solution: [1M 2020]

(A) exchange of atoms takes place

(B) exchange of ions takes place

(D) an insoluble salt is produced

The correct option is:

(a) (B) and (D) (b) (A) and (C)

Answer : (b) (A) and (C) .

Question : In a double displacement reaction such as the reaction between sodium sulphate solution and barium chloride solution :

(i) Exchange of atoms takes place

(ii) Exchange of ions takes place .

(iii) a precipitate is produced .

(iv) an insoluble salt is produced

The correct option is :

(A) (ii) and (iv) (B) (i) and (iii) (C) only (ii) (D) (ii) , (iii) and (iv)

Answer : (D) (ii), (iii), and (iv)

[ In a double displacement reaction such as the reaction between sodium sulfate solution and barium chloride solution:

(ii) Exchange of ions takes place.

(iii) A precipitate is produced.

(iv) An insoluble salt (precipitate) is produced.]

Question : Lead nitrate solution is added to a test tube containing potassium iodine solution .

(a) Write the name and colour of the compound precipitated.

(b) Write the balance chemical equation for the reaction involved .

Answer : (a) The compound precipitated is lead iodide, which is yellow in color.

(b) The balanced chemical equation for the reaction is:

(c) This reaction is a double displacement reaction, also known as a double replacement reaction. In this reaction, the ions in the reactants exchange places to form new compounds. Lead nitrate reacts with potassium iodide to form potassium nitrate and lead iodide. The formation of a precipitate (lead iodide) confirms that it is a double displacement reaction.

Question : What happens when food materials containing fats and oil are left for a long time /list two observable changes and suggest three ways by which this phenomenon can be prevented .

Answer : When food materials containing fats and oils are left for a long time, they undergo a process called rancidity. Two observable changes associated with rancidity are:

(i) The fats and oils develop a disagreeable smell and taste.

(ii) The color of the food may change, often becoming darker.

To prevent the occurrence of rancidity, here are three ways:

(i) Keep the food in airtight containers to minimize exposure to oxygen, which is one of the factors contributing to rancidity.

(ii) Store the food in a refrigerator to slow down the chemical reactions that lead to rancidity. Lower temperatures help preserve the quality of fats and oils.

(iii) Incorporate natural antioxidants or use food preservatives that can help prevent the oxidation of fats and oils. Common antioxidants include vitamin E and certain herbs and spices.

CBSE Previous Years Questions and Answers for 2021

Question : A student took sodium sulphate solution in a test tube and added barium chloride solution to it .He observed that an insolution substance has formed .The colour and molecular formula of the insoluble substance is

(A) Grey , (B) Yellow , (C) White , (D) Pink ,

Answer : (C) White , .

Question : Sodium reacts with water to form sodium hydroxide and hydrogen gas . The balanced equation which represents the above reaction is :

(a)

(b)

(c)

(d)

Answer : (b) .

Question :

The above reaction is a/an

(a) displacement reaction

(b) endothermic reaction

(d) neutralization reaction

Answer : (c) exothermic reaction .

Question : Which of the following statements about the reaction given below are correct ?

(i) HCl is oxidised to

(ii) is reduced to

(iii) acts as an oxidising agent

(iv) HCl acts as an oxidising agent .

(a) (ii) , (iii) and (iv) (b) (i) , (ii) and (iii) (c) (i) and (ii) only (d) (iii) and (iv) only

Answer : (c) (i) and (ii) only .

Question : It is important to balance the chemical equations to satisfy the law of conservation of mass . Which of the following statements of the law is incorrect ?

(a) The total mass of the elements present in the reactions is equal to the total mass of the elements presents in the products .

(b) The number of atoms of each element remains the same, before and after a chemical reaction .

(d) Mass can neither be created nor can it be destroyed in a chemical reaction .

Answer : (c) The chemical composition of the reactants is the same before and after the reaction.

Question : Which one of the following reactions is categorized as thermal decomposition reaction ?

(a)

(b)

(c)

(d)

Answer : (d)

Question : Assertion (A) : Burning of natural gas is an endothermic process .

Reason (R) : Methane gas combines with oxygen to produce carbon dioxide and water .

(a) Both (A) and (R) are true and (R) is the correct explanation of (A) .

(b) Both (A) and (R) are true but (R) is not the correct explanation of (A)

(d) (A) is false, but (R) is true .

Answer : (d) (A) is false, but (R) is true .