Chemical Changes and Reactions Dalal Simplified Class-9 ICSE Chemistry Solutions Chapter-2 . We Provide Step by Step Solutions of Exercise/Lesson -2 Chemical Changes and Reactions with Additional Questions , Previous Year Questions and Unit Test-2 of Dr Viraf J Dalal Middle School Chemistry Allied Publishers. Visit official Website CISCE for detail information about ICSE Board Class-9.

## Chemical Changes and Reactions J Dalal Dr Viraf New Simplified Class-9 ICSE Chemistry Solutions Chapter-2

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### Previous Year Questions of Chapter Chemical Changes and Reactions

#### Question 1.(1986)

Explain : Silver nitrate solution is kept in coloured reagent bottles in the laboratory.

Silver nitrate gets decomposed by sunlight. Hence silver nitrate is stored in coloured reagent bottles.

#### Question 1.(1987)

Give an example of an endothermic reaction.

#### Question 1.(1988)

State in each case if the reaction represents oxidation or reduction

#### Question 1.(1989)

Reactions can be classified as : Direct combination, decomposition, simple displacement, double decomposition, Redox reactions. State which of the following types, takes place in the reactions given below

1. Cl2 + 2KI → 2KCl + l2
2. 2Mg + O2 → 2MgO
3. SO2 + 2H2O + Cl2 → 2HCl + H2SO4
4. AgNO3 + HCl → AgCl + HNO3
5. 4HNO3 → 4NO2 + 2H2O + O2

1. Cl2 + 2KI → 2KCl + I2 — Simple displacement
2. 2Mg + O2 → 2MgO — Direct combination
3. SO2 + 2H2O + Cl2 → 2HCl + H2SO4 — Redox reaction
4. AgNO3 + HCl → AgCl + HNO3 — Double decomposition
5. 4HNO3 → 4NO2 + 2H2O + O2 — Decomposition reaction

#### Question 1.(1990)

Give one reason why magnetizing a piece of steel is a physical change.
There is no change in composition.

#### Question 1.(1993)

State whether the following are oxidation or reduction

### Additional Questions of Chemical Changes and Reactions by Dalal Simplified

#### Question 1.

Explain the term chemical reaction with special reference to reactants and products.
Chemical change : “Is reprsentation of a chemical change in substances taking part and are called reactants written on left side of →

When Zn react with dil HCl, new substance ZnCl and H2 are produced as a result of chemical change reactants are seperated by + sign and products formed are also separated by + sign.

#### Question 2.

Give a suitable example with equation to show the representation of a chemical reaction.
Iron and sulphuric acid dilute which react to produce ferrous sulphate and hydrogen gas can be represented by a chemical equation.
Iron + dil. sulphuric acid → ferruous sulphate and hydrogen

#### Question 3.

A chemical reaction is often accompanied by external indications or characteristics.
Give two examples where a chemical reaction is accompanied by a change in colour of the reactants & products on completion of the reaction.
A chemical reaction is accompanied by change in colour of reactants and products

#### Question 4.

Give balanced equations for reactions involving evolution of a gas on addition of dilute acid to

(a) sodium sulphite
(b) calcium carbonate.

#### Question 5.

Give a balanced equation for conversion of

(a) an ammonium salt to a basic gas
(b) a soluble lead salt to an insoluble lead salt – formed as a white precipitate.

(a) Ammonium salt [NH4Cl] on heating produces NH3(g) which is a basic gas

#### Question 6.

Chemical reactions may proceed with evolution or absorption of heat. Give an example of each.
Chemical reaction is characterised by evolution of heat :

#### Question 7.

Define the following types of chemical changes or reactions with a suitable example each.

(a) Direct combination reaction or synthesis
(b) Decomposition reaction
(c) Displacement reaction or substitution reaction
(d) Double decomposition reaction

##### (a) Direct Combination Reaction Of Synthesis :

“Those reactions in which two or more substances [element or elements and compound or compounds] combine and form a new substance”
H2 + O2 → H2O Hydrogen combines with oxygen to produce a new substance water.
(b) Decomposition Reaction :
“Those reactions in which a compound splits up into two or more simpler substances”

#### Question 8.

Give a balanced equation for a direct combination reaction involving :

(a) Two elements — one of which is a neutral gas and the other a yellow non¬metal
(b) Two elements – one of which is a neutral gas and the other a monovalent metal
(c) Two compounds – resulting in formation of a weak acid

(a) Direct Combination of two elements one of which is a neutral gas and the other a yellow non-metal

#### Question 9.

Give balanced equations for the following reactions of synthesis involving formation of :

(a) An acid – from sulphur dioxide gas
(b) An alkali – from a basic oxide – sodium oxide
(c) A salt – from a trivalent metal and a coloured gas.

#### Question 10.

Convert — (a) nitrogen to ammonia (b) hydrogen to hydrogen chloride – by a direct combination reaction.
By direct combination reaction :
(a) Nitrogen to ammonia

#### Question 11.

Give balanced equations for thermal decomposition of :

(c) ammonium dichromate
(d) mercury [II] oxide
(e) calcium hydroxide

Decomposition of :

#### Question 12.

Define – a thermal dissociation reaction with a suitable example. Give an example of a photochemical decomposition reaction. Name a metallic oxide which on thermal decomposition is reduced to a metal.
Thermal Dissociation :
“A decomposition reaction — in which a substance dissociates — into two or more simpler substances on application of heat.”

#### Question 13.

Define a displacement reaction with a suitable example. State how it is represented. Give a reason why zinc displaces hydrogen from dilute sulphuric acid but copper docs not.
Displacement reaction : “Is a chemical reaction in which an element [or radical] replaces another element in a compound.”

Zinc (more electropositive) and being above [H] in activity series displaces hydrogen from dilute sulphuric acid but copper is below [H] in electrochemical series cannot displace hydrogen from sulphuric acid.

#### Question 14.

Explain the term double decomposition — precipitation reaction. Give a balanced equation for the preparation of two different insoluble lead salts from their salt solutions by — double decomposition — precipitation.
Double decomposition reaction is precipitation reaction.
i. e. in which ppt. is formed
“Reaction between two compounds in aqueous state, to give two new compounds one of which is precipitate (or insoluble).”

#### Question 15.

Explain with the help of balanced equations, how precipitation reactions are used for identifying the positive radicals in three different salts, each having a different cation [positive ion].
Precipitation reactions are used to identify the positive ions from their colours.

#### Question 16.

Define the term – double decomposition – neutralization reaction with a suitable representation.

Convert :

(a) an insoluble base
(b) a soluble base to their respective soluble salts by neutralization reaction.

When acid reacts with a base salt and water are formed and this is called Neutralisation.
Double-decomposition — Neutralisation reaction :
“Is the chemical reaction between two compounds (acid and base) to interchange radicals and produce salt and water.”

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