Alkanes

Question 1

Generic formula for alkanes

Answer 1

C(n)H(2n+2)

Question 2

Describe the bonding of alkanes

Answer 2

Single covalent sigma bond

Fully saturated

Can rotate

Question 3

What is a sigma bond

Answer 3

End to end overlap of orbitals

Single covalent bond

Question 4

Describe the shape of alkanes

Answer 4

Tetrahedral (4 bonds per carbon atom)

Question 5

Bond angle in alkanes

Answer 5

109.5

Question 6

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

Answer 6

BP increases

More surface contact points so stronger London forces

Question 7

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

Answer 7

Decrease BP

Less compact, weaker and fewer London forces

Less surface contact points, weaker London forces

Question 8

Describe the reactivity of alkanes and state why

Answer 8

Lack of reactivity

Due to strong sigma bonds and lack of polar bonds

Question 9

Why are alkanes used as fuels?

Answer 9

Readily available

No toxic byproduct when combusted

Easy to transport

Question 10

What may form in incomplete combustion?

Answer 10

CO or C

(not both)

+H2O

Question 11

Give an example of a substitution reaction with alkanes

Answer 11

+ Halogen

Halogen substitutes H

Question 12

State steps in radical substitution

Answer 12

Initiation

Propagation

Termination

Question 13

Explain radical substitution

Answer 13

A Halogen radical substitutes a H in a hydrocarbon

Question 14

Describe initiation

Answer 14

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

Question 15

What occurs during initiation?

Answer 15

Photodissociation

Question 16

What does hv mean?

Answer 16

Light

Question 17

Describe Propagation

Answer 17

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

Atom from stable goes to radical

Question 18

Describe Termination

Answer 18

Two radicals react to form a stable

Two unpaired electrons form a pair

Question 19

What are the limitations of radical substitution?

Answer 19

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

Substitution of Halogen at different points gives rise to structural isomers

Question 20

Gives two names of Hcl and the conditions

Answer 20

Aqueous = hydrochloric acid

Solid/ gas = hydrogen chloride

Question 21

Define chain reaction

Answer 21

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

Question 22

Why is further substitution not desired?

Answer 22

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