chemistry - fuels (8.1 - 8.17)

8.1 what are hydrocarbons?

compounds that contain carbon & hydrogen only

8.2 what is crude oil?

a complex mixture of hydrocarbons

contains molecules in which carbon atoms are in chains/rings

an important source of useful substances (fuels & feedstock for petrochemical industry)

a finite resource

8.3 separation of crude oil by fractional distillation - why?

crude oil not runny enough/ignited easily enough to be used as fuel

separated into simpler, more useful mixtures

fractional distillation - different hydrocarbons have different boiling points

8.3 separation of crude oil by fractional distillation - how?

in tall metal fractionating column

1. crude oil heated strongly to evaporate it & hot vapours pipped into bottom of column

column is hottest at bottom & coldest at top

2. vapours condense when reach part of column below their boiling point

3. liquid falls into tray & piped away

4. vapours with lowest boiling points don’t condense - leave top as mixture of gases

5. bitumen has highest boiling point - leaves at bottom as hot liquid

8.4 names & uses of fractions: gases

domestic heating & cooking

8.4 names & uses of fractions: petrol

fuel for cars

8.4 names & uses of fractions: kerosene

fuel for aircraft

8.4 names & uses of fractions: diesel oil

fuel for some cars & trains

8.4 names & uses of fractions: fuel oil

fuel for large ships & in some power stations

8.4 names & uses of fractions: bitumen

surface roads & roofs

8.5 properties of fractions

compounds in crude oil fractions are mostly from alkane homologous series

8.6 a homologous series is a series of compounds which…

have same general formula (e.g. alkanes = C_nH_2n+2)

differ by CH₂ in molecular formulae from neighbouring compounds

show gradual variation in physical properties (shown in boiling points)

have similar chemical properties (e.g. alkane + oxygen → carbon dioxide + water)

8.7 complete combustion of hydrocarbon fuels

carbon dioxide + water produced

energy given out

8.8 why can incomplete combustion of fuels produce carbon & carbon monoxide?

some carbon atoms in hydrocarbon may be:

• fully oxidised to carbon dioxide

• only partially oxidised to carbon monoxide

• released as smoke & soot

incomplete combustion of hydrocarbon fuels

happens when limited supply air/oxygen

carbon dioxide + carbon monoxide + water produced

energy given out (less than complete combustion)

8.9 how does carbon monoxide behave as a toxic gas?

combines with haemoglobin in RBCs - prevents oxygen combining

reduces amount of oxygen carried in bloodstream - makes people sleepy/unconscious/can cause death