12.3 - Combustion of alkanes

Question 1

Scrubbing/flue gas desulfurisation process

Answer 1

Calcium oxide can be used:

• Calcium oxide and water reacts with sulfur dioxide to initially produce calcium sulfiite, which is then further oxidised to calcium sulfate or gypsum:
• CaO (s) + 2H2O (l) + SO2(g) + ½O2(g) → CaSO4.2H2O (s)

Calcium carbonate can also be used

• CaCO3+ ½O2(g) + SO2(g) → CaSO4(s) + CO2(g)

Question 2

Removal of NOx gases

Answer 2

• 2CO + O2→ 2CO2

or

• 2CO + 2NO → 2CO2+ N2

Reduction of NO to N2:

• 2CO + 2NO → 2CO2+ N2

Question 3

Effects of oxides of nitrogen

Answer 3

• Nitrogen oxides can also dissolve and react in water with oxygen to form nitric acid which is a cause ofacid rain
• Acid rain can cause corrosion of buildings, endangers plant and aquatic life (as lakes and rivers become tooacidic) as well as directly damaging human health

Question 4

How are oxides of nitrogen formed?

Answer 4

• in a car engine, high temperatures and pressures are reached causing the oxidation of nitrogen to take place:

N2(g) + O2(g) → 2NO(g)

N2(g) + 2O2(g) → 2NO2(g)

Question 5

Effects of carbon monoxide:

Answer 5

CO is a toxic and odourless gas which can cause dizziness, loss of consciousness and eventually death

• The CO binds well to haemoglobin which therefore cannot bind oxygen and carbon dioxide
• Oxygen is transported to organs
• Carbon dioxide is removed as waste material from organs

Question 6

Where does incomplete combustion take place?

Answer 6

Incomplete combustion often takes place inside acar enginedue to a limited amount of oxygen present

With a reduced supply of oxygen,carbonwill be produced in the form of soot:

Question 7

What is incomplete combustion

Answer 7

When alkanes are burnt in only alimited supplyof oxygen,incomplete combustionwill take place and not all the carbon is fully oxidised

Some carbon is onlypartiallyoxidised to formcarbon monoxide

For example, the incomplete combustion of octane to form carbon monoxide

Question 8

What is complete combustion?

Answer 8

When alkanes are burnt inexcess(plenty of) oxygen,complete combustionwill take place and all carbon and hydrogen will be oxidised tocarbon dioxideandwaterrespectively

For example, the complete combustion of octane to carbon dioxide and water