Alkanes Flashcards

1
Q

Generic formula for alkanes

A

C(n)H(2n+2)

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2
Q

Describe the bonding of alkanes

A

Single covalent sigma bond

Fully saturated

Can rotate

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3
Q

What is a sigma bond

A

End to end overlap of orbitals

Single covalent bond

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4
Q

Describe the shape of alkanes

A

Tetrahedral (4 bonds per carbon atom)

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5
Q

Bond angle in alkanes

A

109.5

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6
Q

What effect does increasing the length of the carbon chain have on boiling point? Why?

A

BP increases

More surface contact points so stronger London forces

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7
Q

What affect does increasing branching have on boiling point? Why?

A

Decrease BP

Less compact, weaker and fewer London forces

Less surface contact points, weaker London forces

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8
Q

Describe the reactivity of alkanes and state why

A

Lack of reactivity

Due to strong sigma bonds and lack of polar bonds

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9
Q

Why are alkanes used as fuels?

A

Readily available

No toxic byproduct when combusted

Easy to transport

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10
Q

What may form in incomplete combustion?

A

CO or C

(not both)

+H2O

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11
Q

Give an example of a substitution reaction with alkanes

A

+ Halogen

Halogen substitutes H

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12
Q

State steps in radical substitution

A

Initiation

Propagation

Termination

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13
Q

Explain radical substitution

A

A Halogen radical substitutes a H in a hydrocarbon

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14
Q

Describe initiation

A

Covalent bond in Halogen is broken by homolytic fission is presence of UV radiation

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15
Q

What occurs during initiation?

A

Photodissociation

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16
Q

What does hv mean?

A

Light

17
Q

Describe Propagation

A

A stable and radical react to form a different stable and radical

Atom from stable goes to radical

18
Q

Describe Termination

A

Two radicals react to form a stable

Two unpaired electrons form a pair

19
Q

What are the limitations of radical substitution?

A

Further substitution of H with Halogen leads to undesired haloalkanes (multiple Halogen groups)

Substitution of Halogen at different points gives rise to structural isomers

20
Q

Gives two names of Hcl and the conditions

A

Aqueous = hydrochloric acid

Solid/ gas = hydrogen chloride

21
Q

Define chain reaction

A

When a species is used up in one reaction and then produced in a second one leading to a cycle of the two reactions

22
Q

Why is further substitution not desired?

A

Produces a mixture of structural isomers which are costly and time consuming to seperate