Topic 7- organic chemistry:

Question 1

What are hydrocarbons?

Answer 1

Any compound that is formed form hydrogen and carbon atoms only.

Question 1

Alkanes:

Answer 1

• The simplest type of hydrocarboon you can get
• General formula- C(n)H(2n+2)
• They are a homoglous series- group of organic compounds that work in similar ways
• They are saturated compunds- each carbon atom forms 4 bonds
• First 4- Methane, Ethane, Propane, Butane. (Monkeys Eat Peanut Butter)

Question 2

Properties of hydrocarbons:

Answer 2

• Properties of hydrocarbons change as the carbon chain gets longer
• The shorter the carbon chain, the more runny and less viscous (gloopy) it is
• The shorter the carbon chain, the more voaltile the hydrocarbon is- lower it’s boiling point
• The shorter the hydrocarbon, the more flammable it is
• They are burnt so they can be used as fuel as the reaction produces energy

Question 3

Complete combustion:

Answer 3

• Occurs when there is a lot of oxygen
• Complete combustion of any hydrocarbon releases lots of enegy- waste products are CO2 and water
• Hydrocarbon + oxygen 🡒 carbon dioxide + water (+energy)
• During combustion, both the hydrogen and carbon from the hydrocarbon are oxidised

Question 4

Crude oil:

Answer 4

• A finite resource found in rocks
• A fossil fuel form the remains of ancient biomass- mainly of plankton buried in mud
• Turned to crude oil due to high temperature and high pressure
• A mixture of lots of different hydrocarbons (mostly alkanes)
• Different compounds can be seperated using farctional distillation

Question 5

Fractional distillation:

Answer 5

• The oil is heated until most of it turns into gas, the gases enter the fractionating collumn
• In the colllumn, the temperature is hotter at the bottom and cooler at the top
• Longer hydrocarbons have higher boiling points. Shorter hydrocarbons have lower boiling points
• So they will condense at different levels in the tower

Question 6

What are the uses of crude oil?

Answer 6

• Provides the fuel for modern transport
• The petrochemical industry uses some hydrocarbbons from crude oil as feedstock to make new compounds for use in polymers, solvents, lubricants and detergenets
• All products from crude oil are an example of organic compund (they contain carbon atoms)

Question 7

Cracking:

Answer 7

Cracking means splitting up long-chain hydrocarbons
* This is because short-chain hydrocarbons are flammable so make good fuels and are high in demand
* As a result, the longer alkane molecules produced by fractional distillation are turned into smaller, more useful ones by cracking.

Question 8

Processes of cracking:

Answer 8

Cracking is a thermal decomposition reaction-breaks molecules diwn by heating them
* The long-chain hydrocarbons must be heated to vaporise them
* Then either catalytic cracking or steam cracking take place.

Question 9

Process of catalytic cracking:

Answer 9

Pass them over a hot catalyst and the long-chain molecules split apart on the surface

Question 10

Process of steam cracking:

Answer 10

Mix them with steam and heat them to a very high temperature so that thermal decomposition reactions can occur

Question 11

General equation for cracking:

Answer 11

Long chain hydrocarbon molecule → shorter alkane molecule + alkene