Chapter 1 Chemical Reactions and Equations

NCERT Class 10th

Science SOLUTIONS

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Question

What does one mean by exothermic and endothermic reactions? Give examples.

Updated on June 28, 2025 | By Learnzy Admin | 👁️ Views: 466 students

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Exothermic & Endothermic reactions refer to the flow of energy (usually in the form of heat) during a chemical reaction.

Exothermic Reactions:

An exothermic reaction releases energy, usually in the form of heat, to its surroundings. In these reactions, the energy of the products is lower than that of the reactants. For example:

Combustion (burning) of fuel like methane:-- CH₄ + 2O₂ → CO₂ + 2H₂O + energy (heat)
In this reaction, energy is released as heat when methane burns.

Endothermic Reactions:

An endothermic reaction absorbs energy from the surroundings. In these reactions, the energy of the products is higher than that of the reactants. For example:

Photosynthesis in plants:-- 6CO₂ + 6H₂O + energy (sunlight) → C₆H₁₂O₆ + 6O₂
Plants absorb sunlight to convert carbon dioxide and water into glucose and oxygen.

In summary:

Exothermic = Energy released (e.g., burning fuels).
Endothermic = Energy absorbed (e.g., photosynthesis).

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More Questions on `Chemical Reactions and Equations`

Question 1

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

Question 2

In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the reaction involved.

Question 3

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

Question 4

Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity.

Question 5

Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions

Question 6

Why is respiration considered an exothermic reaction? Explain

Question 7

What is a balanced chemical equation? Why should chemical equations be balanced?

Question 8

What happens when dilute hydrochloric acid is added to iron fillings? Tick the correct answer. (a) Hydrogen gas and iron chloride are produced. (b) Chlorine gas and iron hydroxide are produced. (c) No reaction takes place. (d) Iron salt and water are produced

Question 9

Fe₂O₃ + 2Al → Al₂O₃ + 2Fe The above reaction is an example of a (a) combination reaction. (b) double displacement reaction. (c) decomposition reaction. (d) displacement reaction.

Question 10

Identify the substances that are oxidised and the substances that are reduced in the following reactions. (i) 4Na(s) + O2(g) → 2Na2O(s) (ii) CuO(s) + H2(g) → Cu(s) + H2O(l)

Question 11

Why does the colour of copper sulphate solution change when an iron nail is dipped in it?

Question 12

A solution of a substance ‘X’ is used for whitewashing. (i) Name the substance ‘X’ and write its formula. (ii) Write the reaction of the substance ‘X’ named in (i) above with water.

Question 13

Write a balanced chemical equation with state symbols for the following reactions. (i) Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride. (ii) Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution and water

Question 14

Write the balanced equation for the following chemical reactions. (i) Hydrogen + Chlorine → Hydrogen chloride (ii) Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride (iii) Sodium + Water → Sodium hydroxide + Hydrogen

Question 15

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

Question 16

A solution of substance ‘X’ is used for white washing. What is the substance ‘X’? State the chemical reaction of ‘X’ with water.

Question 17

Hydrogen being a highly inflammable gas and oxygen being a supporter of combustion, yet water which is a compound made up of hydrogen and oxygen is used to extinguish fire. Why?

Question 18

What is meant by a chemical reaction?

Question 19

1 g of copper powder was taken in a China dish and heated. What change takes place on heating? When hydrogen gas is passed over this heated substance, a visible change is seen in it. Give the chemical equations of reactions, the name and the colour of the products formed in each case.

Question 20

Oil and fat containing food items are flushed with nitrogen. Why?

Question 21

A shiny brown coloured element ‘X’ on heating in air becomes black in colour. Name the element ‘X’ and the black coloured compound formed.