Hydrocarbons at Room Temperature

Gas Methane Ethane Propane Butane

Plastic Liquid Waxy20 to 40 Carbons5 to 19

Carbons

40 or more Carbons

Melting Point As the length of hydrocarbons get longer, the

Melting Point grows Higher. Why?

0 5 10 15 20 25 30 35 40 45-300

-200

-100

0

100

200

300

400

500

600

Melting and Boiling Temperatures of Alkanes

Boiling Point (˚C)

Melting Point(˚C)

Number of Carbons

Tem

pura

ture

(˚C

)

What other material properties change?

Viscosity

Hardness

Toughness

Flammability

Physical Properties of Hydrocarbons

• The first four alkanes (C1 to C4) are all gases at room temperature.

• Compounds from C5 to C17 are oily liquids. • Compounds greater than C17 are solids at room

temperature and pressure.• As the number of carbon atoms increases, the

molecules become larger and heavier. This also means that their melting points and boiling points increase.

• Liquid alkanes are insoluble in water, are less dense than water. Alkanes are soluble in non-polar solvents.

Reactions of hydrocarbons

• Complete Combustion (oxidation) reactions

Alkanes, alkenes and alkynes burn in air reacting with the oxygen in air to produce carbon dioxide and water.

CH4(g) + 2O2(g) ® CO2(g) + H2O(g)• Incomplete combustion (oxidation)

reactions produces carbon monoxide and water vapour.

Reactions of alkanes• Substitution reactions

Alkanes react with halogens in sunlight or at high temperature in a substitution reaction.

Substitution continues if more halogens are present.

Su

S

UV light

• Alkanes

Reactions of the alkenes & alkynes• When alkenes or alkynes react with halogens

they undergo addition reactions.

Naming hydrocarbons

Functional Groups

Functional groups

• Functional groups are parts of molecules that result in characteristic features.

Name Group Naming

Halo alkanes -X The number of the carbon atom to which the halogen has been bonded must be given followed by the halogen and then the prefix indicating the number of carbons in the chain.

Alkanols -OH Alkanols have the ending -ol.

Carboxylic group

-COOH add the ending -oic acid to the alkyl prefi x.

Ester the alkanol (alkyl) name is given first, followed bythe acid part. The -oicending of the acid is replaced with -oate.

Amines -NH2 the suffix -amine to the alkane group to whichthe —NH2 has been added

Esters

• The carboxylic acids react with alkanols to form esters. Esters are a group of compounds which give the pleasant ‘fruity’ smell to various fruits. This is called a dehydration or esterification reaction.

Name and draw the expanded structural formula of the ester formed whenethanol reacts with propanoic acid.• .

Crude oil

• Crude oil, also called petroleum, is a complex mixture of carbon and hydrogen (hydrocarbons), which exist as a liquid in the earth's crust.

• The carbon and hydrogen in crude oil are thought to have originated from the remains of microscopic marine organisms that were deposited at the bottom of seas and oceans and was transformed at high temperature and pressure into crude oil and natural gas.

Petroleum Refining

• Petroleum refining is the process of separating the many compounds present in crude petroleum. This process is called fractional distillation where the crude oil is heated; the various of the compounds boil at different temperatures and change to gases; and are later recondensed back into liquids.

• The principle which is used is that the longer the carbon chain, the higher the temperature at which the compounds will boil.

Fractional distillation

properties

The various components of crude oil have different sizes, weights and boiling temperatures and viscocity

• bigger the molecule greater the intermolecular force• ... more viscous as the intermolecular attractive forces

between molecules increases. • ... higher melting point as more vibrational kinetic energy is

needed to overcome the intermolecular attractive forces holding the molecules together to form the crystals.

• ... less flammable as they become less volatile, again due to increasing intermolecular forces.

Cracking

• Cracking is the name given to breaking up large hydrocarbon molecules into smaller and more useful bits. This is achieved by using high pressures and temperatures without a catalyst(thermal cracking), or lower temperatures and pressures in the presence of a catalyst(catalytic cracking).