Alkanes

Define a petroleum fraction

A mixture of hydrocarbons with a similar chain length and boiling point range

Describe fractional distillation (key points)

Oil is pre heated then passed into column

Fractions condense at different heights

Temperature of column decreases upwards

Separation depends on boiling point which depends on size of molecules (van der waaals)

Similar molecules (size, bp, mass) condense together

Small molecules at top, big at bottom at higher temps

Which type of forces are broken during fractional distillation?

Van der Waals between molecules

Define cracking

The conversion of large hydrocarbons to smaller hydrocarbon molecules by breakage of C-C bonds

Give the economic reasons for cracking

Petroleum fractions with shorter C chains are more in demand, makes use of excess larger hydrocarbons, products are more valuable than starting materials

Give the two types of cracking

Thermal and catalytic

Give the conditions needed for thermal cracking

High pressure (7000 kPa), high temperature (400-900°C)

What are the major products of thermal cracking?

Alkenes (sometimes hydrogen)

Give the conditions needed for catalytic cracking

Slight pressure, high temperature (450°C), zeolite catalyst

What are the major products of catalytic cracking?

Branched and cyclic alkanes, aromatic hydrocarbons

Define a fuel

Releases heat energy when burnt

What are the products of complete combustion?

H2O + CO2

What are the products of incomplete combustion?

CO and/or C and H2O

When does incomplete combustion occur?

When there is insufficient oxygen

Where are Sulfur-containing impurities found?

In petroleum fractions

What do Sulfur impurities produce when burnt?

SO2

Give the environmental implications of SO2 in the atmosphere

SO2 will dissolve in atmospheric water and can produce acid rain

How can SO2 be removed from the waste gases from furnaces?

By flue gas desulfurisation

Describe flue gas desulfurisation

Gases pass through a scrubber containing basic calcium oxide which reacts with the acidic Sulfur dioxide in a neutralisation reaction

Give the equation for flue gas desulfurisation

SO2 + CaO —> CaSO3

How do nitrous oxides form?

From the reaction between N2 and O2 inside car engines - high temperature and spark in the engine provides sufficient energy to break strong N2 bond

Give the equations for the formation of nitrous oxides in car engines

N2 + O2 —> 2NO or N2 + 2O2 —> 2NO2

Give the environmental consequences of nitrous oxides

NO is toxic and can form acidic gas NO2, NO2 is toxic and acidic and forms acid rain

Give the environmental consequences of carbon monoxide

Toxic - inhibit bloods ability to carry oxygen around body

Give the enviromental consequences of carbon dioxide

Contributes towards global warming

Give the environmental consequences of unburnt hydrocarbons

Contributes towards formation of smog

Give the environmental consequences of soot *

Global dimming and respiratory problems

Describe the role of catalytic converters

Remove CO, NOx and unburned hydrocarbons from the exhaust gases, turning them into ‘harmless’ CO2, N2 and H2O

Describe the structure of a catalytic converter

Have a ceramic honeycomb coated with a thin layer of catalyst metals, (platinum, palladium, rhodium) to give a large surface area

Describe how carbon dioxide contributes towards global warming

The C=O bonds absorb infrared radiation from the Earth and prevent it from escaping the atmosphere, then the energy is transferred to other molecules in the atmosphere by collisions so the atmosphere is warmed

What conditions does free radical substitution initiation require?

UV light

Give the steps of free radical substitution

Imitation, propagation, termination

Give the equation for initiation step of FRS

Cl2 —> 2 *Cl

By what process does the Cl-Cl bond break by in initiation?

Homolytic fission

Define a free radical

A reactive species which possesses an unpaired electron (don’t have any charge)

Give the proportion steps in FRS using methane + Cl2

CH4 + Cl —> Cl + *CH3

*CH3 + Cl2 —> CH3Cl + *Cl

Give the equation for termination during FRS using methane and Cl2

*CH3 + *Cl —> CH3Cl

2 *CH3 —> CH3CH3