Alkanes

What happens during fractional distillation?

• Crude oil is heated to vaporise it

• The vapour is passed into the column

• The top of the tower is cooler than the bottom (negative temperature gradient)

• Fractions are separated out by their bpt

• Low bpt fractions collected at the top

What is cracking?

I process where long chain hydrocarbons are broken into smaller chain hydrocarbons

Requirements and results of thermal cracking?

• High temp (1200K)

• High pressure (7000Kpa)

• Large proportion of alkenes and lower proportion of branched alkanes

Requirements and results of catalytic cracking?

• Relatively low temp (700K)

• Slightly above atmospheric pressure

• Large proportion of branched alkanes and arenes

• Uses a zeolite catalyst

Why is zeolite a good catalyst?

It’s structure gives it a high surface area

What is the solid pollutant in incomplete combustion?

Carbon (soot)

What is the gaseous pollutant in incomplete combustion?

Carbon monoxide

How is nitrogen monoxide formed and what is the equation showing this?

• Temperatures in internal combustion engines can reach very high temperatures over 2000^oC

• Strong N₂ triple covalent bonds are broken

• This allows nitrogen and oxygen to react

N₂ + O₂ → 2NO

How is nitrogen dioxide formed from combustion engines?

• NO can further react with oxygen to produce NO₂

NO + 1/2O₂ → NO₂

How is nitric acid formed and what affect does this have on the environment?

• Nitrogen dioxide can react with rain water and more oxygen to produce nitric acid which contributes to acid rain

2NO₂ + H₂O + 1/2O₂ → 2HNO₃

What are the effects of acid rain?

• Corrodes buildings

• Lowers pH of rivers and streams, affecting photosynthesis, killing plants eventually leading to the death of fish

• Lowers the pH of soil which can affect microorganisms and crops

What is the release of unburnt hydrocarbons linked to?

Cancer

What are catalytic converters and what are they made of?

• Used to transform pollutants gasses in a car’s exhaust into less harmful gasses

• Contains a honeycomb structure for a high surface area

Equation for the removal of CO in a catalytic converter

CO + ½ O₂ → CO₂

Equation for the removal of CO and NO in a catalytic converter

CO + NO → CO₂ + ½ N₂

Equation for the removal of NO in a catalytic converter

2NO → N₂ + O₂

Equation for the removal of unburnt hydrocarbons in a catalytic converter

Hydrocarbon + Oxygen → Carbon dioxide + water

Basically a combustion equation

Equation for the removal of unburnt hydrocarbons and NO in a catalytic converter

Hydrocarbon + NO→ CO₂ + N₂ + H₂O

How do catalytic converters work?

• NO is adsorbed by the catalyst

• Attaches to surface forming weak IMF

• This weakens the bond within the molecule so it is broken

• Nitrogen and Oxygen desorbed from the catalyst and IMFs disappear

Why is sulfur impurities in fossil fuels a problem and where does it come from?

• It burns in oxygen to produce SO₂

• It can be further oxidised into SO₃

• Both of these can react with water to form sulfurous and sulfuric acid

Equations for the formation of sulfur dioxide and sulfur trioxide

• S + O₂ → SO₂

• SO₂ + ½ O₂ → SO₃

Equations for the formation of sulfurous acid and sulfuric acid

• SO₂ + H₂O → H₂SO₃

• SO₃ + H₂O → H₂SO₄

How can sulfur dioxide be remove from flue gasses?

• Flue gas desulphurisation

• S reacts with calcium oxide or calcium carbonate and is neutralised

What are the equations that show what happens in lue gas desulphurisation?

• CaO + SO₂ → CaSO₃

• CaCO₃ + SO₂ → CaSO₃ + CO₂