Chemistry 9th Chap 14 : Topic 2 - Maryam Publications

Chemistry Chapter 14 : Topic 2

Chemical Properties of Alkanes

1 / 20

Which statement best explains why alkanes are generally considered unreactive under normal conditions?

A) They have strong ionic bonds between carbon and hydrogen atoms.

B) They consist of only single covalent (sigma) bonds which are relatively stable and non-polar.

C) They contain double bonds that easily break and react.

D) They readily gain electrons due to high electronegativity difference.

2 / 20

Although alkanes are generally unreactive, they still undergo combustion. Which explanation best justifies this exception?

A) Alkanes decompose spontaneously without oxygen.

B) Combustion requires breaking ionic bonds in alkanes.

C) Alkanes contain chlorine which supports combustion.

D) Oxygen reacts with alkanes under suitable conditions producing energy.

3 / 20

Which condition is essential for substitution reaction of methane with chlorine?

A) Presence of catalyst like iron

B) High pressure and water

C) UV light or sunlight

D) Electric current

4 / 20

In the substitution reaction of alkanes with chlorine, what is the main product formed?

A) Carbon dioxide and water

B) Chloroalkane and hydrogen chloride

C) Alcohol and water

D) Alkene and hydrogen gas

5 / 20

Why do alkanes not react easily with acids, bases, or oxidizing agents under normal conditions?

A) They have strong polar bonds.

B) They are ionic compounds.

C) They contain free electrons.

D) They lack functional groups and have stable non-polar covalent bonds.

6 / 20

Which statement correctly describes complete combustion of alkanes?

A) It produces carbon monoxide and water.

B) It produces carbon and hydrogen gas.

C) It produces carbon dioxide and water with energy release.

D) It produces chlorine and hydrogen chloride.

7 / 20

What is observed during incomplete combustion of alkanes?

A) No flame is produced

B) Formation of carbon monoxide and soot

C) Formation of only carbon dioxide

D) Blue flame with maximum energy

8 / 20

Which property of alkanes makes them suitable as fuels despite being chemically unreactive?

A) They are toxic and highly reactive.

B) They form ionic compounds easily.

C) They are insoluble in water and non-reactive but release large energy on combustion.

D) They easily polymerize at room temperature.

9 / 20

During chlorination of methane, why is the reaction described as a substitution reaction?

A) Hydrogen atom is replaced by chlorine atom.

B) Methane breaks into smaller molecules.

C) Chlorine is added without removing any atom.

D) Carbon atom is replaced by chlorine atom.

10 / 20

Which feature of alkanes mainly contributes to their low chemical reactivity?

A) Presence of triple bonds

B) High polarity of molecules

C) Saturated structure with single bonds only

D) Presence of double bonds

11 / 20

What happens when methane reacts with chlorine in the presence of sunlight for a long time?

A) Only one product is formed.

B) Methane turns into ethene.

C) No reaction occurs.

D) Multiple substitution products can form.

12 / 20

Which statement best compares alkanes with alkenes regarding reactivity?

A) Both are equally reactive in all conditions.

B) Alkanes are less reactive due to lack of double bonds.

C) Alkanes are more reactive due to double bonds.

D) Alkenes are less reactive due to saturation.

13 / 20

Why does combustion of alkanes release energy?

A) Chlorine atoms release energy during reaction.

B) Energy is absorbed to form bonds in products.

C) Alkanes contain stored electrical energy.

D) Energy is released when new stronger bonds form in CO₂ and H₂O.

14 / 20

Which observation indicates that combustion of an alkane is incomplete?

A) No flame at all

B) Formation of chlorine gas

C) Clean blue flame and no smoke

D) Yellow smoky flame with soot deposition

15 / 20

Why are alkanes considered saturated hydrocarbons?

A) They contain oxygen atoms in structure.

B) They contain double bonds.

C) They contain maximum possible hydrogen atoms bonded to carbon.

D) They are soluble in water.

16 / 20

Which condition is NOT required for combustion of alkanes?

A) Heat or ignition source

B) Oxygen

C) UV light

D) Fuel (alkane itself)

17 / 20

In chlorination of alkanes, what initiates the reaction mechanism?

A) Breaking of carbon-carbon double bonds

B) Homolytic cleavage of Cl₂ producing free radicals

C) Formation of ions in water

D) Formation of hydrogen gas first

18 / 20

Which property explains why alkanes do not decolorize bromine water under normal conditions?

A) They are acidic in nature.

B) They contain oxygen.

C) They are saturated and do not undergo addition reactions easily.

D) They are ionic compounds.

19 / 20

What is the main environmental concern associated with incomplete combustion of alkanes?

A) Increase in nitrogen concentration

B) Production of oxygen gas

C) Formation of water vapor only

D) Release of carbon monoxide, a poisonous gas

20 / 20

Which statement best summarizes the chemical behavior of alkanes?

A) Always form ionic compounds

B) Highly reactive due to unsaturation

C) Generally unreactive but undergo combustion and substitution under specific conditions

D) React vigorously with water

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