12.1-12.2 -properties Of The Alkanes/ Chemical Reactions

Question 1

What is an alkane?

Answer 1

A saturated hydrocarbon containing C-H bonds only

Question 2

Are alkane bonds polar? Why?

Answer 2

Non-polar because carbon and hydrogen have similar electronegativities

Question 3

What is the shape and angle of an alkane ?

Answer 3

Tetrahedral - 109.5°

Question 4

Describe the sigma bond in an alkane

Answer 4

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

Question 5

What type of intermolecular forces do alkanes have? Why?

Answer 5

London forces - induced dipole-dipole interaction as the bonds are nonpolar

Question 6

What happens to the boiling point as alkane chain length increases? Why?

Answer 6

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

Question 7

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

Answer 7

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

Question 8

Are alkanes soluble in water?

Answer 8

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

Question 9

How reactive are alkanes?

Answer 9

Very unreactive

Question 10

What reactions will alkanes undergo?

Answer 10

Combustion and reaction with halogens

Question 11

What type of reaction is combustion?

Answer 11

Oxidation reaction

Question 12

Define complete combustion

Answer 12

Combustion that occurs with plentiful supply of air

Question 13

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

Answer 13

Carbon dioxide and water

Question 14

Define incomplete combustion and the products formed in case of alkanes?

Answer 14

Combustion in a limited supply of oxygen
Products - water , carbon dioxide and carbon monoxide

Question 15

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

Answer 15

Longer chains

Question 16

What are the 3 stages of free radical substitution?

Answer 16

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

Question 17

What is the main use of alkanes?

Answer 17

Fuels as they make up natural gas and crude oil

Question 18

Describe the bonding in alkanes

Answer 18

• Saturated hydrocarbons with only single bonds between carbon atoms
• each carbon atoms form 4 sigma bonds

Question 19

Hour does a sigma bond form?

Answer 19

• The overlap of 2 orbitals, one from each bonding atom
• each overlapping orbital contains one electron resulting in 2 electrons shared between bonding atoms

Question 20

Why are alkanes relatively unreactive?

Answer 20

• the C-C and C-H sigma bonds are strong
• the C-C bonds are non polar
• the electronegativity of C and H are similar so C-H is so considered non polar

Question 21

Why is carbon monoxide dangerous?

Answer 21

It is colourless, odourless and tasteless and can be fatal as it is a toxic gas