08/04/2023

Formation of oil and gas

1) Layers of dead sea _____ settle on the seabed.

2) Layers of __________ rock build up on top.

3) The heat and ________ from these rocks, along with the absence of ______, mean that oil and gas are formed over ______ of years.

Words – sedimentary, millions, oxygen, creatures, pressure

08/04/2023Hydrocarbons and crude oil

Longer chains

mean…

1. Less ability to flow

2. Less flammable

3. Less volatile

4. Higher boiling

point

Incre

asin

g le

ng

th

Crude oil is a mixture of HYDROCARBONS (compounds made up of carbon and hydrogen). Some examples:

Ethane

C C

HH

H

HH

H

Butane

C C

HH H

HH

H C C H

H

HH

08/04/2023

Fractional distillationCrude oil can be separated by fractional distillation. The oil is evaporated and the hydrocarbon chains of different lengths condense at different temperatures:

Fractions with low boiling

points condense at

the top

Fractions with high boiling

points condense at the bottom

08/04/2023

CrackingShorter chain hydrocarbons are in greater demand because they burn easier. They can be made from long chain hydrocarbons by “cracking”:

Butane

Ethane

Ethane

For example, this bond can be

“cracked” to give two of these:

08/04/2023Cracking

This is a THERMAL DECOMPOSITION reaction, with clay used as a catalyst

1) Carbon dioxide causes the _________ effect

2) Sulphur dioxide causes _____ _____

3) Plastics are not _____________

Cracking is used to produce plastics such as polymers and polyethanes. The waste products from this reaction include carbon dioxide, sulphur dioxide and water vapour. There are three main environmental problems here:

08/04/2023

AlkanesAlkanes are SATURATED HYDROCARBONS. What does this mean?

HYDROCARBONS are molecules that are made up of hydrogen and carbon atoms

SATURATED means that all of these atoms are held together by single bonds, for example:

Ethane Butane

Alkanes are fairly unreactive (but they do burn well).

08/04/2023

AlkenesAlkenes are different to alkanes; they contain DOUBLE COVALENT bonds. For example:

Ethane Ethene

Butane Butene

This double bond means that alkenes have the potential to join with other molecules – this make them REACTIVE. We can test for alkenes because they turn bromine water colourless.

ALK

AN

ES

ALK

EN

ES

08/04/2023

Monomers and Polymers

Ethene

Here’s ethene again. Ethene is called a MONOMER because it is just one small molecule. We can use ethene to make plastics…

Step 1: Break the double bond

Step 2: Add the molecules together:

This molecule is called POLYETHENE, and the process that made it is called POLYMERISATION

08/04/2023

Another way of drawing it…Instead of circles, let’s use letters…

Ethene

C C

HH

HH

C C

HH

HH

Ethene

H

C C

H

HH

H

C C

H

HH

Poly(e)thene

General formula for addition polymerisation:

C Cn C C

n

e.g. C Cn

H CH3

HH

C Cn

H CH3

HH