Chapter 12

Question 1

Features of crude oil

Answer 1

Fossil fuel- made from decaying plants and animals from millions of years ago
Does not ignite easily
Must be separated to become useful

Question 2

What kind of bond do alkanes contain and what does it allow them to do

Answer 2

A sigma bind
Acts as a axis so the atoms can rotate freely so the shapes aren’t rigid

Question 3

How does the chain length of alkanes effect the boiling point

Answer 3

As chain length increases there are more points of contact leading to more London forces between the molecules, therefore the higher the boiling point

Question 4

How does branching in alkanes effect the boiling point

Answer 4

Branched molecules have fewer points of contact and are further apart then unbranched molecules so there are fewer intermolecular forces so the boiling point decreases as the branches increase

Question 5

Do alkanes react with common reagents and why

Answer 5

No
C-C and C-H sigma bonds are strong
C-C bonds are non polar
The electronegativity of carbon and hydrogen is so similar that the C-H bond can be considered to be non polar

Question 6

What are short chain alkanes valuable for

Answer 6

Clean fuels eg natural gas or LPG (liquified propane and butane)

Question 7

Complete combustion of petrol

Answer 7

Mainly octane
C8H18(l) + 12.5O2(g) ———> 8CO2(g) + 9H2O(l)

Question 8

Incomplete combustion of petrol

Answer 8

C8H18(l) + 8.5O2(g) ———> 8CO(g) + 9H2O(l)

Question 9

Properties of carbon monoxide

Answer 9

Colourless odourless highly toxic
Binds IRREVERSIBLY with haemoglobin and prevents oxygen from binding so tissues become starved of oxygen

Question 10

Conditions for the reaction between Alkanes and halogens

Answer 10

Presence of UV
300 degrees

Question 11

What happens when an alkane reacts with a halogen in the right condition and an example

Answer 11

Radical substitution reaction :
Covalent bonds broken by Homolytic fission to form radicals with an unpaired electron
A hydrogen atom in the alkane is substituted by a halogen atom
CH4 +Cl2 ———>CH3Cl + HCl
(Bromine reacts in a similar way)

Question 12

Mechanism for chlorination
Step 1

Answer 12

Initiation
The Cl-Cl bind is broken by Homolytic fission to produce radicals
Cl-Cl——> Cl. + Cl.

Question 13

Mechanism for chlorination
Step 2

Answer 13

Propagation
A chain reaction, continues until no reactants remain
CH4 + Cl. ———> .CH3 + HCl
.CH3 + Cl2 ———> CH3Cl + Cl.

Question 14

Limitations of radical substitution

Answer 14

Other mono substituted products are made
Further multiple substitutions occur

Question 15

Mechanism for chlorination
Step 3

Answer 15

Termination
Two radicals combine to form a molecule
Cl. + Cl. ——> Cl2
.CH3 + .CH3 ——> C2H6
. CH3 + . Cl ——> CH3Cl