Alkanes

Question 1

What is the general formula for alkanes?

Answer 1

CnH2n+2

Question 2

Are alkanes saturated or unsaturated?

Answer 2

They are saturated.

Question 3

What is the shape of alkanes?

Answer 3

Tetrahedral

Question 4

How many pairs of bonding electrons surround each carbon atom?

Answer 4

4

Question 5

How do the bonding electrons repel each other?

Answer 5

They repel each other equally.

Question 6

What is the bond angle of alkanes?

Answer 6

109.5

Question 7

What are the properties of short alkanes?

Answer 7

Low boiling point

Gases at RTP

Question 8

In what state are larger alkanes?

Answer 8

They are liquids.

Question 9

What type of bonds are inside alkane molecules?

Answer 9

Covalent bonds.

Question 10

What type of bonds are between the alkane molecules?

Answer 10

London forces

Question 11

What do the London forces do to the molecules?

Answer 11

They hold them all together.

Question 12

What increases the strength of the London forces?

Answer 12

The longer the carbon chain,the stronger the induced dipole-dipole interactions.

Question 13

Why do the induced dipole-dipole interactions get stronger as the carbon chain gets longer?

Answer 13

There is more surface contact and more electrons to interact.

Question 14

Why does the boiling point rise as the carbon chain gets longer?

Answer 14

It takes more energy to overcome the London forces.

Question 15

Why do branched-chain alkanes have lower boiling points than their straight-chain isomers?

Answer 15

They can’t pack together as closely so there is a smaller molecular surface area, this reduces the strength of the London forces.

Question 16

What happens if you oxidise alkanes?

Answer 16

You get carbon dioxide and water.

Question 17

Do alkanes react completely in oxygen?

Answer 17

Yes

Question 18

In what state do the combustion reactions of alkanes occur?

Answer 18

In gas.

Question 19

What needs to happen to liquid alkanes before combustion?

Answer 19

They need to be vaporised.

Question 20

What burns more easily, long chain alkanes or short chain alkanes?

Answer 20

Short chain alkanes as they are gases.

Question 21

What is more volatile, long chain alkanes or short chain alkanes?

Answer 21

Short chain alkanes.

Question 22

Why do larger alkanes release more energy per mole?

Answer 22

They have more bonds to react.

Question 23

Why do alkanes make excellent fuels?

Answer 23

They release lots of energy when they burn.

Question 24

What do all gases at the same temperature and pressure have in common?

Answer 24

Thy have the same molar volume when at the same temperature and pressure.

Question 25

What can you use to calculate the molar ratios when atoms are at the same temperature and pressure?

Answer 25

You can use the ratio of the volumes of the gases reacting.

Question 26

What happens as a result of incomplete combustion?

Answer 26

Carbon monoxide and water is formed.

Question 27

What is the problem with carbon monoxide?

Answer 27

It binds to the haemoglobin before the oxygen can, this means that less oxygen is carried around in the body and therefore you can get oxygen deprivation.