4.1.2: Alkanes Flashcards

1
Q

What is an alkane?

A

A saturated hydrocarbons containing

C-H bonds only

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2
Q

What is the general formula of an alkane?

A

CnH2n+2

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3
Q

Are alkane bonds polar? Why/why not?

A

Nonpolar because carbon and hydrogen have similar electronegativities

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4
Q

What is the shape and angle of an alkane?

A

Tetrahedral

109.5°

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5
Q

Describe the 𝜎 bond in alkane

A

The sigma bond is a covalent bond which has a direct overlap of the electron clouds of the bonding atoms.

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6
Q

What type of intermolecular forces do alkanes have? Why?

A

London force → induced dipole-dipole interaction, because the bonds are nonpolar

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7
Q

What happens to the boiling point as alkane chain length

increases? Why?

A

The boiling point increases because there is more surface area and so more number of induced dipole- dipole interaction. Therefore more energy required to overcome the attraction

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8
Q

Does a branched molecule have lower or higher boiling point compared to equivalent straight chain? Why?

A

The branched molecule has a lower boiling point because they have fewer surface area and hence less induced dipole -dipole interactions.

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9
Q

Are alkanes soluble in water? Explain your answer.

A

Insoluble because hydrogen bonds in water are stronger than alkanes’ London forces of attraction

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10
Q

How reactive are alkanes?

A

Very unreactive

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11
Q

What reactions will alkanes undergo?

A

Combustion and reaction with halogens

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12
Q

What type of reaction is combustion?

A

Oxidation reaction

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13
Q

What is complete combustion?

A

Combustion that occurs with plentiful supply of air

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14
Q

What are the products of complete combustion when alkanes are used?

A

Carbon dioxide and water

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15
Q

What is the colour of the bunsen burner flame during complete combustion?

A

Blue flame

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16
Q

What is incomplete combustion and what products are formed in the case of alkanes?

A

Combustion in a limited supply of oxygen

Products : water, carbon dioxide and carbon monoxide

17
Q

Write an equation for the combustion of propane

A

C3H8 + 5O2 → 3CO2 + 4H2O

18
Q

Which type of hydrocarbon are most likely to undergo incomplete combustion?

A

Longer chains

19
Q

What is the environmental impact of carbon monoxide?

A

It is toxic/poisonous

20
Q

What is the environmental impact of soot (carbon)?

A

Asthma, cancer, global dimming

21
Q

How are halogenoalkanes formed from alkanes?

A

Radical substitution

22
Q

In the presence of what does alkane react with halogens?

A

UV light

23
Q

What are the three stages of free radical substitution?

A

Initiation - breaking halogen bond to form free radicals
Propagation - chain part of the reaction where prod s are formed but free radical remains
Termination - free radicals removed, stable products formed

24
Q

Write equations for the reaction of CH4 with Cl2 to form CH3Cl

A

Initiation: Cl2→ 2Cl• (in presence of UV light)
Propagation: Cl• + CH4 → HCl + •CH3
•CH3 + Cl2 → CH3Cl + Cl•
Termination:•CH3 + Cl• → CH3Cl 2Cl• → Cl2
•CH3+ •CH3→ CH3CH3