Chemical Reactions and Equations

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Class 10 Science Chapter 1
Chemical Reactions and Equations
Important Questions

Introduction

Chapter 1 of Class 10 Science, Chemical Reactions and Equations covers chemical equations, balanced chemical equations, implications of balanced chemical equations, and many types of chemical reactions. For instance, combination, decomposition, displacement, double displacement, precipitation, endothermic exothermic processes, oxidation, and reduction. The Consequences of Oxidation Reactions in Everyday Life, such as Rancidity and Corrosion.

Class 10 Chemical Reactions and Equations, Important Questions and Answers

Q 1. When hydrogen sulphide gas is passed, 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:
Options
(a) Combination reaction
(b) Displacement reaction
(c) Decomposition reaction
(d) Double displacement reaction

Ans. (d)

Explanation:
Double displacement is a type of chemical reaction where two compounds react, and the positive ions (cation) and the negative ions (anion) of the two reactants switch places, forming two new compounds or products.
H_2S + CuSO_4 → CuS + H_2SO_4

Q 1. On the basis of evolution or absorption of heat, chemical reactions can be divided into how many types?
Options
(a) Two
(b) Three
(c) Four
(d) One

Ans. (a) Two

Explanation:

Chemical reactions can be divided into 2 types on the basis of evolution or absorption of heat in a chemical reaction.
1) Exothermic Reactions - The chemical reactions in which energy is evolved either in the form of light or heat.
Example- CaCl_2 (s) + 2(H_2O) \rightarrow Ca(OH)_2 (aq) + 2 HCl (g) + heat.
2) Endothermic Reactions - The chemical reactions in which energy is absorbed either in the form of heat or light.
Example- 6CO_2 (g) + 6 H_2O (g) + heat \rightarrow C_6H_{12}O_6 + 6O_2 (g).

Q3. Why is it advisable to show the physical states of substance when writing a chemical equation?

Explanation:
It is advisable to show the physical state of the substance to make it more informative and to emphasise that those reactions occur in that manner only under those conditions. Hence, physical states of reactants and products are mentioned while writing a chemical equation.

Q4. What happens when magnesium ribbon burns in air?

Explanation:
When magnesium ribbon burns in air, it combines with the oxygen to form magnesium oxide.
2Mg(s) + O_2(g) \rightarrow 2MgO(s)

Q5. Write chemical equation reactions taking place when carried out with the help of: Excess of carbon dioxide gas is passed through lime water.

Explanation:
Lime water is solution of Calcium Hydroxide almost as clear as water When Carbon dioxide gas is passed through it it turns milky because in this chemical reaction Calcium Carbonate is Formed which is insoluble in water So these insoluble particles are spread throughout the solution These particles being white in colour the solution appears to be milky.
When excess CO_2 is added, it reacts with calcium carbonate ( CaCO_3) and water (H_2O) to form calcium bicarbonate Ca(HCO_3)_2 and since it is soluble in water, it dissolves in it making the solution clear again.
\\Ca(OH)_2(ag) + CO_2 (g) \rightarrow CaCO_3(s) + H_2O(I)\\[4.5 bp] CaCO_3(s) + H_2O(I) + CO_2(g) \rightarrow Ca(HCO_3)_2(aq)

CBSE Class 10 Science Chapter wise Important Questions

Conclusion

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Frequently Asked Questions

Ans: A chemical reaction takes place when two or more molecules meet in the proper direction and with enough force to create a new product. Bonds between atoms are broken and formed during this process. Reactants are substances that interact to form new substances, whereas products are the newly created substances.
Ans: Combustion, decomposition, neutralisation, redox, precipitation or double-displacement, and synthesis are some of the numerous types of reactions that might occur depending on the product that is produced.
Ans: When molecules in a reactant undergo a chemical reaction, their bonds are broken, and molecules in the product undergo a similar process, new bonds are created, creating a new substance. The production of a chemical product from reactants is represented mathematically by a chemical equation.
Ans: The breakdown of chemical species into less complex components is known as a decomposition reaction.Example: When heated, calcium carbonate breaks down into calcium oxide and carbon dioxide.
CaCO3 (s) + Heat → CaO (s) + CO2 (g)
Ans: Two reactants exchange ions to generate two new compounds in a displacement reaction known as precipitation or a double displacement reaction. Example: AB + CD → AD + CB