Chapter 12 Alkanes

Question 1

What are alkanes?

Answer 1

Saturated hydrocarbons, containing only carbon and hydrogen atoms joined together by single covalent bonds

Question 2

How are alkanes separated from crude oil?

Answer 2

Fractional distillation in a distillation tower

Question 3

What are the effects of increasing chain length on the boiling point of alkanes

Answer 3

• Increased chain length
• Greater surface are of contact
• Stronger / more london forces to overcome
• Boiling point therefore increases

Question 4

What are the effects of branching on the boiling points of alkanes?

Answer 4

• More branching
• Less surface area of contact
• Weaker london forces

Question 5

Why are alkanes unreactive?

Answer 5

Alkanes only contain C–C and C–H bonds which are both strong non-polar bonds that won’t readily react

Question 6

List the three stages of radical substitution

Answer 6

Stage 1: Initiation
Stage 2: Propagation
Stage 3: Termination

Question 7

Describe the initiation stage during radical substitution

Answer 7

• Bromine molecule broken by homolytic fission
• Each bromine takes one electron from the bond
• Forms two highly reactive bromine radicals

Question 8

Describe the propagation stage during radical substitution

Answer 8

Firstly a bromine radical reacts with a C–H bond in the methane, forming a methyl radical, and a molecule of hydrogen bromide

Secondly, each methyl radical reacts with another bromine molecule, forming the organic product bromomethane, together with a new bromine radical

Question 9

Describe the termination stage during radical substitution

Answer 9

Two radicals collide, forming a molecule with all electron pairs