topic 8 - fuels and earth science

Question 1

what are hydrocarbons

Answer 1

compounds containing only hydrogen and carbon

Question 2

what is crude oil

Answer 2

• a complex mixture of hydrocarbons which have carbons atoms in chains and rings
• it is a finite resource
• it is a source of useful substances

Question 3

names and uses of the fractions from top to bottom

Answer 3

gases: domestic heating and cooking
petrol: car fuel
kerosene: aircraft fuel
diesel oil: fuel in some cars and trains
fuel oil: fuel for large ships and in some power stations
bitumen: surfaces roads and roofs

Question 4

properties of short vs long hydrocarbons

Answer 4

shorter = less viscous, lower boiling temp, more flammable (bc they’re gases and easier to ignite)

Question 5

hydrocarbons as a homologous series

Answer 5

• they have the same general formula
• they differ bu CH2 in molecular formula from neighbouring compounds
• show a gradual variation in physical properties
• have similar chemical properties

Question 6

complete combustion of hydrocarbon fuels

Answer 6

CO2 and H2O are produced, it’s exothermic

Question 7

incomplete composition of hydrocarbons

Answer 7

some of the fuel doesn’t burn in insufficient oxygen - solid particles of soot (carbons) and unburnt fuel are released
• soot causes global dimming

CO is released where there isn’t enough oxygen to produce CO2
• CO causes health problems

Question 8

hydrocarbon fuels and sulfur dioxide

Answer 8

most fuels contain carbon+/hydrogen and may also contain some sulfur

when burnt in oxygen this sulfur can react to form sulfur dioxide

when sulfur dioxide dissolves in rainwater, acid rain forms:

• damages statues and buildings made of limestone
• reduces growth of/kills trees and crops
• lowers pH of water in lakes, killing fish

Question 9

why are oxides of nitrogen formed when fuels are burned in engines

Answer 9

nitrogen and oxygen from the air combine to form nitrogen monoxide

when nitrogen monoxide is released from vehicle exhaust systems, it combines with oxygen in the air to form nitrogen dioxide

both of these are pollutants

Question 10

pros and cons of using hydrogen as car fuel instead of petrol

Answer 10

+ petrol is from crude oil, a finite resource
+ only produces water, no CO2, Co or soot

• it needs a special, expensive engine
• manufacturing hydrogen gas is expensive and needs energy from another source which often involves fossil fuels
• hard to store and transport
• it can be explosive

Question 11

what is methane and where is it found

Answer 11

a non-renewable fossil fuel found in natural gas

Question 12

what is cracking and how is it done

Answer 12

the breaking down of larger, saturated hydrocarbon molecules (alkanes) into smaller unsaturated alkene molecules that are more useful

the hydrocarbons are heated to vaporise them

the vapours are passed over a very hot catalyst / mixed with steam and heated to a very high temp so that thermal decomposition reactions can occur

Question 13

alkenes

Answer 13

have the general formula Cn H2n, theyre unsaturated as they have a double bond

the first 2 are ethene and propene

Question 14

earths early atmosphere

Answer 14

• the earths surface was originally molten for millions of years, there was almost no atmosphere
• eventually the surface cooled and a crust formed, but volcanoes kept erupting releasing gases from inside the earth
• this released mainly CO2 but also steam, methane and ammonia
• the earths atmosphere was initially mostly CO2 and water vapour with very little oxygen

• the water vapour later condensed to form oceans

Question 15

how was CO2 first removed from the atmosphere

Answer 15

a lot of the early CO2 dissolved into the oceans

then green plants evolved and photosynthesised, removing CO2 and most of the CO2 was trapped in fossil fuels and sedimentary rocks

Question 16

how did N2 in the atmosphere increase

Answer 16

N2 was released by denitrifying bacteria and formed by ammonia reacting with oxygen

Question 17

the evolution of complex animals

Answer 17

increase in oxygen killed of organisms that couldn’t tolerate it but allowed the evolution of more complex organisms that made use of the oxygen

oxygen also formed the ozone layer which blocked harmful rays from the sun and enabled even more complex animals to form

Question 18

test for oxygen

Answer 18

check if the gas can relight a glowing splint

Question 19

what are greenhouse gases

Answer 19

the gases in the atmosphere that can absorb and reflect heat radiation

Question 20

how are current global temps and CO2 levels worked out

Answer 20

by using measurements worldwide

Question 21

getting historical climate data

Answer 21

historical data isn’t very accurate - less data was taken and with fewer location and the methods were less accurate

ways to estimate it - tree rings, ice cores etc
but these are much less precise than current measurements made with instrumental sampling + much less representative of global levels