Concise Class-9 Chemical Changes and Reactions Ch-2 Selina ICSE Solutions

Revised Concise Selina Chemistry Solutions Chapter-2 ICSE Board Class 9

Concise Class-9 Chemical Changes and Reactions Selina ICSE Solutions Chapter-2 . Step by Step Selina Concise Solutions for ICSE Class-9 Chemistry of Chapter-2 . The Solutions of Exercise-2(A), Exercise-2(B) and Exercise-2(C) Questions of Ch-2 Chemical Changes and Reactions. Visit official website cisce for detail information about icse class -9 Chemistry.

Concise Class-9 Chemical Changes and Reactions Selina ICSE Solutions Chapter-2


Select topics 

 Exercise-2(A),

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 Exercise-2(B)

 Exercise-2(C).


Make self written Notes on following topics

  • Chemical change
  • Characteristics of chemical change
  • Types of chemical reactions
  • Energy change in chemical reactions
  • Photochemical reaction
  • Electrochemical reaction

Exercise-2(A),Chemical Changes and Reactions Selina Solutions for ICSE Class 9 Chemistry                        

Question 1

(a) What is a chemical reaction?

(b) State the conditions necessary for a chemical change or reaction. 

Answer 1

(a) A chemical reaction is the process of breaking the chemical bonds of the reacting substances (reactants) and making new bonds to form new substances (products).

(b) Conditions necessary for a chemical change or reaction are

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(i) Evolution of gas

(ii) Change of colour

(iii) Formation of precipitate

(iv)Change of state

Question 2

Define the following terms

(a). Chemical bond

(b). Effervescence

(c). Precipitate

Answer 2 

(a). A chemical bond is the force which holds the atoms of a molecule together as in a compound.

(b). Formation of gas bubbles in a liquid during a reaction is called effervescence.

(c). Chemical reactions which are characterised by the formation of insoluble solid substances are called precipitates.

Question 3

Give an example of a reaction where the following are involved

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(a) Heat

(b) Light

(c) Electricity

(d) Close contact

(e) Solution

(f) Pressure

(g) Catalyst

Answer 3 

defferent type of reaction

Question 4

Define

(a) Photochemical reaction

(b) Electrochemical reaction

Give an example in each case.

Answer4

(a) It is a reaction which occurs with absorption of light energy.

(b) It is a reaction which occurs with absorption of electrical energy.

Question 5

Give an example of each of the following chemical changes:

(a) A photochemical reaction involving

(i) Silver salt (ii) water

(b)A reaction involving

(i) Blue Answer

(ii) Formation of dirty green precipitate

(c)Two gases combine to form white solid

(d)Two solids combine to form a liquid

(e)A reaction where colour change is noticed

Answer 5

selina-icse-solutions-class-9-chemistry-chemical-changes-reactions-5

Question 6

Write the chemical reaction where the following changes are observed.

(a) Gas is evolved

(b) Colour change is noticed

(c) Precipitate is formed

(d) Physical state is changed

Answer 6

selina-icse-solutions-class-9-chemistry-chemical-changes-reactions-6

 

Question 7

Give reason for the following:

(a) Silver nitrate Answer is kept in coloured bottles.

(b) Molybdenum is used in the manufacture of ammonia.

(c) Blue Answer of copper sulphate changes to green when a piece of iron is added to this solution.

(d) Colourless concentrated sulphuric acid in a test tube changes to blue on adding a small piece of copper to it.

Answer 7

(a)Silver nitrate Answer is kept in brown bottles in the laboratory because it decomposes in the presence of light.

(b)Molybdenum increases the efficiency of the catalyst iron used in the manufacture of ammonia.

(c)This is because the blue colour of the copper sulphate Answer fades and eventually turns into light green due to the formation of ferrous sulphate.

(d)Copper displaces hydrogen from sulphuric acid and forms blue-coloured copper sulphate and hydrogen gas is evolved.


 Exercise-2(B), Selina Concise Chemistry Solutions ICSE Class 9 Chapter-2  

Question 1

Complete the following statements:

(a)The chemical change involving iron and hydrochloric acid illustrates a _________________ reaction.

(b)In the type of reaction called_______________, two compounds exchange their positive and negative radicals.

(c)A catalyst either ______ or _____________ the rate of a chemical change but itself remains ______________ at the end

Of the reaction.

(d)On heating, hydrated copper sulphate changes its colour from ________ to __________.

Answer 1

(a)Displacement

(b)Double decomposition

(c)Accelerates, decelerates, unaffected

(d)Blue, white

Question 2

When hydrogen burns in oxygen, water is formed; when electricity is passed through water, hydrogen and oxygen are given out. Name the type of chemical change involved in the two cases.

Answer 2

When hydrogen burns in oxygen, water is formed – Combination Reaction.

When electricity is passed through water, hydrogen and oxygen are given out – Decomposition Reaction.

Question 3

Explain, giving one example for each of the following chemical changes:

(a) Double decomposition

(b) Thermal decomposition

(c) Reversible reaction

(d) Displacement

Answer 3

(a) Double decomposition reaction

This is a type of chemical change in which two compounds in a Answerreact to form two new compounds by mutual exchange of radicals

(b) Thermal decomposition

A decomposition reaction brought about by heat is known as thermal decomposition.

2HgO(s)  2Hg(s) +O2(g) 

(c) Reversible reaction

A chemical reaction in which the direction of a chemical change can be reversed by changing the conditions under which the reaction is taking place is called a reversible reaction.

CuSO4.5H2O(s) ⇋ CuSO4(s) + 5H2O (g) 

(d) Displacement Reaction

It is a chemical change in which a more active element displaces a less active element from its salt solution.

CuSO4 + Zn → ZnSO4 + Cu

Question 4 

(a) What is synthesis?

(b) What kind of chemical reaction is synthesis? Support your answer by an example.

Answer 4

A reaction in which two or more substances combine together to form a single substance is called a synthesis or combination reaction.

A + B → AB

In the above reaction, substances A and B combine to give a molecule of a new substance, AB.

Carbon burns in oxygen to form a gaseous compound, carbon dioxide.

C + O2 == CO2

Question 5

Decomposition brought about by heat is known as thermal decomposition. What is the difference between thermal dissociation and thermal decomposition?

Answer 5

A decomposition reaction brought about by heat is known as thermal decomposition.

2HgO(s)  —- 2Hg(s) + O2 (g)

A simultaneous reversible decomposition reaction brought about only by heat is thermal dissociation.

NH4Cl ⇋ NH3 +HCl

Question 6

(a)Define neutralization reaction with an example.

(b)Give balanced equation for this reaction.

(c)Give three applications of neutralization reactions.

Answer 6 

(a)The reaction between an acid and a base to form salt and water only is referred to as a neutralisation reaction.

(b)NaOH + HCl → NaCl + H2O

(c)   Applications of neutralisation reactions:

(i) When someone is stung by a bee, formic acid enters the skin and causes pain, which can be relieved by rubbing the spot with slaked lime or baking soda, both of which are bases.

(ii)  Acid which is accidentally spilled on to our clothes can be neutralised with ammonia solution.

(iii) If soil is somewhat acidic and thus unfavourable for growing of certain crops, slaked lime is added to neutralise the excess acid.

Question 7

What do you understand by precipitation reaction? Explain with an example.

Answer 7

A chemical reaction in which two compound in their aqueous state react to form an insoluble salt (a precipitate) as one of the product is known as precipitation reaction.

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