7 organic chemistry

Question 1

define crude oil

Answer 1

crude oil is a finite resources formed over a million years a go from the remains for animal and plants.

Question 2

define hydrocarbon

Answer 2

hydrocarbons are compounds made from only hydrogen and carbon

Question 3

define alkanes

Answer 3

alkanes are:

• saturated compounds
• single covalent bonds

Question 4

name the first four alkanes

Answer 4

Methane
Ethane
Propane
Butane

Question 5

what is the formulae for alkanes?

Answer 5

2n+2

Question 6

How is fractional distillation used in crude oil?

Answer 6

Fractional distillation separates the hydrocarbons with different boiling points in crude oil. The process helps separate the hydrocarbons into fractions.

Question 7

define fraction

Answer 7

a fraction is a group of molecules with similar boiling points

Question 8

explain the process of fractional distillation in crude oil

Answer 8

1- The crude oil is heated and vaporised
2- The vaporised crude oil enters the fractionating tower
hotter at top cooler at bottom
3- The hydrocarbons cool as they rise up the tower and condense at different heights due to different boiling points.
4- The hydrocarbons with large molecules are collected as liquids at the bottom
5- The hydrocarbons with small molecules are collected as liquids at the top

Question 9

what are the fractions from crude oil used for?

Answer 9

The fractions from crude oil can be used for:

• cars
• petrol for vehicles
• making chemicals
• jet fuel
• diesel for cars and lorries
• lubricating oils
• fuel for ships
• central heating
• roads and roofing

They can be used as feed stock for processes to make useful substances like the above.

Question 10

When alkanes burn, they react with oxygen. so combustion occurs. there are 2 types of combustion. what are they?

Answer 10

The two types of combustion that occur when alkanes burn are complete combustion and incomplete combustion.

Question 11

Give the formulae for complete combustion and incomplete combustion

Answer 11

complete combustion:
alkane + oxygen = carbon dioxide + water

incomplete combustion:
1- alkane + oxygen = carbon monoxide + water
2- alkane + oxygen = carbon + water

Question 12

Explain the properties of alkanes depending on the sizes of the molecules

Answer 12

alkanes:
flammability- how easily a substance catches fire
viscosity- how easily a liquid flows

small alkanes:

• low boiling points
• runny
• easy to ignite
• burns with clean flame

large alkanes:

• high boiling points
• viscous
• harder to ignite
• burns with smoky flame

Question 13

define cracking

Answer 13

cracking is the thermal decomposition of long alkanes into shorter alkanes and alkenes.

Question 14

why is cracking useful?

Answer 14

cracking is useful as it breaks down longer alkanes into smaller alkanes this is useful because shorter alkanes are highly in demand as fuels but longer alkanes are in less demand.

Question 15

There are two types of cracking. what are they?

Answer 15

the two types of cracking are:

• catalytic cracking
• steam cracking

Question 16

explain the process of catalytic cracking

Answer 16

heat the alkanes to vaporise them and then pass them over a hot catalyst

Question 17

explain the process of steam cracking

Answer 17

heat the alkanes to vaporise them, mix them with steam and then heat them to a very high temperature

Question 18

define alkenes

Answer 18

alkenes are:

• unsaturated compounds
• double covalent bonds

Question 19

name the first four alkenes

Answer 19

Ethene
Propene
Butene
Pentene

Question 20

what is the formulae for alkenes?

Answer 20

2n

Question 21

which is more reactive, alkenes or alkanes and why?

Answer 21

alkenes are more reactive than alkanes as they contain a double covalent bond while alkanes contain single covalent bonds.

Question 22

describe what happens when alkenes reaction with oxygen

Answer 22

when alkenes react with oxygen they:

• burn in the air with a smoky flame due to incomplete combustion
• are very valuable so can be used to make polymers or used for chemicals.

Question 23

describe the reaction of alkenes

Answer 23

The double bond breaks open and atoms add onto the two carbon atoms. The double bond becomes a single bond so a saturated molecule is produced.

Question 24

describe the reaction of alkenes with halogens

Answer 24

The double bond opens up and one halogen atom adds onto each of the carbon atoms in the double bond

Question 25

describe the reaction of alkenes with hydrogen

Answer 25

The hydrogen atoms add onto the carbon atoms in the double bond. This converts an unsaturated alkene into a saturated alkene.

Question 26

describe the reaction of alkenes with steam

Answer 26

The water atoms are added onto the carbon atoms in the double bond.