Organic Chemistry - Hydrocarbons and Crude oil

Hydrocarbon

Hydrocarbons are compounds/molecules that are made up of carbon and hydrogen only.

Alkanes

• saturated hydrocarbons

• this means no more hydrogen atoms can be added

• all carbon-carbon bonds are single covalent bonds

Rules for carbon and hydrogen bonding

• Carbon - Max 4 covalent bonds (can be double)

• Hydrogen - Max 1 covalent bond

General formula of an alkane

C_nH_2n+2

Homologus series

• Group of organic molecules/compounds that have

• Similar chemical properties

• Due to them all having the same functional group/general formula

Properties of Hydrocarbons

→boiling point
→volatility
→viscosity
→flammability

What are properties of hydrocarbons dependent on?

• the size of the molecule

Boiling point

temperature at which a liquid evaporates to form a gas

Viscosity

• measure of a liquid's resistance to flow

• (how thick or runny a liquid is)

Flammability

• How easily a substance combusts.

• If very flammable means it is easy to burn and catches fire easily

Small vs Long Hydrocarbons

Long

• High BP

• High Viscosity

• Less Volatile

• Less flamable - smoky flame (due to incomplete combustion)

Short

• Low BP

• Flow more easily

• More volatile

• More flammable

Complete combustion of hydrocarbons

• hydrocarbon+oxygen —> carbon dioxide +water vapour (+ energy)

• plentiful supply of oxygen

• carbon and hydrogen in fuel completely oxidised

Prefixes for carbon and n0. correlation

• Meth - 1

• Eth - 2

• Prop - 3

• But - 4

• Pent - 5

• Hex - 6

Draw Alkanes Table

DRAW

Types of Formula

• Displayed

• Gernal

• Molecular

• Structural

Why are longer hydrocarbons less flammable?

• There are strong intermolecular forces between the molecules, which require more energy to overcome.

• This makes them less volatile, meaning they evaporate less easily

• so they produce fewer flammable vapours to mix with the air and are harder to ignite

Incomplete combustion

→ limited supply of oxygen
→ carbon monoxide and/or carbon (soot) also produced

How to test for products of complete combustion of a hydrocarbon

→ Carbon dioxide turns limewater cloudy
→ Water turns blue cobalt chloride paper pink

Crude oil

• It is finite resource

• It is non renewable

• It is a mixture of many different compounds (separated by fractional distillation)

• Made up mostly of hydrocarbons (majority are alkanes)

• Crude oil produces Many of the fuels on which we depend for our modern lifestyle

How was crude oil formed?

• Formed by remains of PLANKTON and dead plants and animals

• That were buried in mud (compressed under mud)

• Over millions of years

• These organic remain were then subject to compressed under extreme pressure and heat

• The heat and pressure chemically changed the organic remains into crude oil

Fractional distillation process

• Crude oil is heated

• Hydrocarbons and liquids evaporate/vaporise into a gas

• Which is passed into the fractionating column

• That has a TEMPERATURE GRADIENT

• When hydrocarbons reach a temperature lower than their boiling point they condense into a liquid

• Fractions collect at different levels depending on their boiling point

• (Longer condense at the bottom as it is hotter and shorter at the top where it is cooler)

What are fractions of crude oil used for (PETROCHEMICAL INDUSTRY)

• Many useful materials on which modern life depends are produced by the petrochemical industry

• Fuels

• Feedstocks - used to make new compounds

  • Polymer

  • Solvent

  • Lubricants

  • Detergents

In terms of boiling point from lowest to highest list products of fractionating

LPG
Petrol
Kerosene
Diesel
Heavy Fuel
Bitumen

Cracking

• Process by which you break down longer hydrocarbon chains into smaller more useful hydrocarbons

• Thermal Decomposition Reaction

Why crack hydrocarbons?

→ some heavier fractions from fractional distillation of crude oil are not in high demand
→ these hydrocarbons are made up of large molecules that are difficult to vaporise and difficult to burn
→ this means that they are poor fuels
→ so are broken down into smaller, more useful hydrocarbons via cracking

Two types of cracking

→ catalytic cracking
→ thermal cracking

Catalytic cracking

• long chain alkanes are heated until they vaporise into a gas

• The gaseous alkanes are passed over hot aluminium oxide catalyst/zeolite catalyst at 500degrees (high temp)

• Break the long chain alkanes into shorter chain alkane and alkene
  

Steam cracking

→ heat fraction/long chain alkane until the vaporise into a gas
→ mix vapour with steam at high temperature (800-900 degrees)

no catalyst involved

Product of Cracking

• Alkanes + Alkenes

Isomers

Isomers are molecules that have the same molecular formula, but different structural formulas, this means they are made of the same atoms, but the atoms are arranged differently

What does saturated mean when talking about hydrocarbons

• Saturated means there are no carbon carbon double bonds

What are short chain alkanes used for?

• Fuels

Why are hydrocarbons used as fuels?

They release a large amount of energy when combusted

Volatility

• Refers to how easily a substance vaporises/evaporates into a gas

• (very volatile means it easily evaporates and gives off fumes)

Is combustion an exothermic or endothermic reaction?

• Combustion is an exothermic reaction as it releases heat energy to the surroundings

• combustion of hydrocarbon fuels releases energy

Why does viscosity increase as chain length increases?

• Viscosity increases because longer molecules can tangle together.
  There are stronger intermolecular forces, so the molecules flow less easily.

Why does boiling point increase as chain length increases?

• Boiling point increases as the number of carbon atoms increases

• Because the intermolecular forces increase

• These intermolecular forces increase as the size of the molecule increases

• More energy is needed to overcome these forces.

Which hydrocarbons make good fuels?

• Shorter hydrocarbons - Very flammable and volatile so easy to combust for energy

• Longer hydrocarbons - Not very flammable or volatile so they are hard to combust for energy

• These properties influence how hydrocarbons are used as fuels

Feedstocks

A feedstock is a raw material used to provide reactants for an industrial reaction.

Petrochemicals

A petrochemical is a substance made from crude oil, via chemical reactions.

What is the use of bitumen?

• Road surfacing

• As it is very viscous

What is the use of the fuels in CRUDE OIL

• Heavy fuel oil - (fuel for ships)

• Diesel Oil - Fuel for diesel vehicles

• Kerosene - Aircraft fuel

• Petrol - Fuel for cars

• LPG - Bottled gas for heating and cooking

Why is there a vast array of natural and synthetic carbon compounds?

• Carbon atoms form four covalent bonds.

• They bond to other carbon atoms to form chains and rings.

• This allows the formation of homologous series.

• Members of a homologous series have the same functional group, same general formula, and similar chemical properties.
  Therefore, carbon forms a very large number of different compounds.

Why are the products of cracking useful?

• Shorter hydrocarbons make better fuels

• Shorter alkanes can also be used as feedstock for the petrochemical industry to make polymers and detergents

What type of reaction is cracking an example of?

• Cracking is a thermal decomposition reaction

Alkenes

• Alkenes are also hydrocarbons and also an example of a homologous series.

• Alkenes have a carbon double bond

• Alkenes are unsaturated

Why cant there be an alkene called methne?

• Methene is only one carbon atom and alkenes are made from two carbon atoms forming a double bond

What is the test for alkenes?

• Bromine water test

• Bromine water by itself is a bright orange colour

• When alkenes are present it decolourises the bromine

• Causing it to turn colourless

Which is more reactive alkanes or alkenes and why?

• Alkenes are more reactive than alkanes.

• Alkenes contain a carbon–carbon double bond (C=C).

• The double bond makes them more reactive

What is the purpose of cracking?

Hydrocarbons can be broken down (cracked) to produce smaller, more useful molecules.

What are the products of cracking used for?

• There is a high demand for fuels with small molecules and so some of the products of cracking are useful as fuels.

• Alkenes are used to produce polymers and as starting materials for the production of many other chemicals.

How Modern Life Depends on Hydrocarbons

Cracking is useful because it breaks long-chain hydrocarbons into shorter-chain hydrocarbons, which are in higher demand as fuels. It also produces alkenes used to make polymers.
Modern life depends on hydrocarbons because they are used as fuels for transport, heating and electricity, and as feedstock for making plastics and other chemicals.

Why is cracking useful?

• Breaks long-chain hydrocarbons

• Produces short-chain fuels

• Matches supply and demand

• Produces alkenes

• Alkenes make polymers

How does modern life depend on hydrocarbons?

• Fuels for transport

• Heating and electricity

• Raw materials (feedstock)

• Used to make plastics and chemicals

Why is there more demand for short-chain hydrocarbons?

• They are more useful as fuels

• More flammable

• Lower boiling points

• Used in petrol

First 4 Alkenes

• Ethene

• Propene

• Butene

• Pentene

Alkene General Formula

CnH2n