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HKDSE Chemistry > 25: Fossil Fuels > Flashcards

25: Fossil Fuels Flashcards

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1
Q

What are the most common energy sources in Hong Kong?

A

Electricity (55%), oil and coal products like petroleum and diesel (28%), town gas and liquefied petroleum gas (LPG) (17%)

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2
Q

What is the source of coal, petroleum, and natural gas?

A

Coal was formed from dead plants while petroleum and natural gas were formed from dead sea creatures.

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3
Q

Why are fossil fuels called non-renewable resources?

A

Fossil fuels are still forming year slowly, but humans are using them up much faster than they can form, meaning that they will run out one day.

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4
Q

How is coal formed?

A

Ancient giant plants die and form thick layers over the swamps. Water and dirt began to pile up on top of the dead plant remains. Over millions of years, high pressure, high temperature, and bacteria action changed these remains into coal.

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5
Q

How are petroleum and natural gas formed?

A

Ancient marine plants and animals die and sink to the seabed. Their remains were covered by layers of sand and sediment. Over time, further deposits of sand and sediment buried the remains deeper and deeper. Over millions of years, high pressure, high temperature, and bacteria action turn the remains into petroleum and natural gas.

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6
Q

What is the definition of hydrocarbon?

A

A hydrocarbon is a compound containing only hydrogen atoms and carbon atoms.

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7
Q

What is the molecular formula of ethene?

A

C2H4

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8
Q

What is the molecular formula of benzene?

A

C6H6

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9
Q

What is the molecular formula of cyclopentane?

A

C5H10

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10
Q

What is the molecular formula of butane?

A

C4H10

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11
Q

What is the condensed structural formula of butane?

A

CH3CH2CH2CH3
or CH3(CH2)2CH3

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12
Q

What are aromatic hydrocarbons?

A

An aromatic hydrocarbon is a hydrocarbon with at least one benzene ring in it structure.

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13
Q

What are aliphatic hydrocarbons?

A

An aliphatic hydrocarbon is a hydrocarbon with no benzene rings; the chains of carbon atoms may be straight or branched, or with rings that are not benzene rings.

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14
Q

List three major classes of hydrocarbons found in petroleum.

A

Alkanes, cycloalkanes, aromatic hydrocarbons

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15
Q

What are saturated hydrocarbons?

A

A saturated hydrocarbon has the maximum possible number of hydrogen atoms in their molecules since all carbon-carbon bonds in the molecule are single covalent bonds.

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16
Q

List two classes of saturated hydrocarbons.

A

Alkanes and cycloalkanes.

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17
Q

What is the general molecular formula of alkanes?

A

CnH2n+2

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18
Q

What is the general molecular formula of cycloalkanes?

A

CnH2n

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19
Q

What are petrochemicals?

A

Petrochemicals are chemicals that are derived from petroleum.

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20
Q

Name 8 products made from petrochemicals.

A

Adhesives, cosmetics, pharmaceuticals, shampoo and shower gel, paints, synthetic rubber, textiles, synthetic polymers

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21
Q

How and where is petroleum separated into fractions?

A

Petroleum is separated into different fractions by fractional distillation, carried out in an oil refinery.

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22
Q

Why should petroleum be processed before it is used as a fuel?

A

When petroleum is burned directly, a lot of black smoke (soot) and harmful gases are produced. Therefore, it cannot directly be used as a fuel and it must be refined first.

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23
Q

How is industrialised fractional distillation of petroleum carried out?

A
  1. Petroleum is first heated to about 400°C in a furnace near the bottom of the fractionating tower.
  2. The mixture of liquid and vapour rises, passing into the tower which is cooler at the top.
  3. The vapour of hydrocarbons pass up the tower via a series of trays containing bubble caps. Rising vapour condenses into liquid when it reaches the tray at a temperature just below its boiling point.
  4. The larger hydrocarbons have a higher melting point, so they condense lower in the tower; smaller hydrocarbons condense at higher, cooler levels.
  5. The substances at each level is then collected separately as fractions of petroleum. Refinery gases leave the top of the fractionating column as gases, while bitumen is collected as a residue at the base of the tower.
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24
Q

How is fractional distillation of synthetic crude oil carried out in a school laboratory?

A
  1. Add mineral wool soaked with synthetic crude oil to a test tube. Place a thermometer to monitor the temperature. Connect it to a delivery tube leading to another test tube in an ice water bath.
  2. Clamp the set-up and heat it with a Bunsen flame gently.
  3. Collect the fractions in the test tube, and when the temperature increases to the desired range, swap the test tube to collect a new fraction.
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25
Q

What are the trends in properties of petroleum fractions?

A

The higher the boiling point of the fraction:
1. the more the carbon atoms in one molecule of hydrocarbon in the fraction
2. the darker the colour
3. the higher the viscosity
4. the lower the volatility
5. the lower the flammability
6. the more sooty the flame when burnt

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26
Q

What is viscosity?

A

Viscosity is how sticky/thick a liquid is. The higher the viscosity, the thicker the liquid.

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27
Q

What is volatility?

A

Volatility is a measure of how easy a liquid evaporates. The higher the volatility, the easier for it to evaporate.

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28
Q

As we go down the fractionating tower, what is the change in the length and boiling points of hydrocarbons condensed?

A

The lower the position, the larger the hydrocarbon molecules, the higher the boiling points.

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29
Q

List the 8 major petroleum fractions in the order of increasing molecular size, and their boiling point ranges.

A
  1. Liquefied Petroleum Gas (LPG / refinery gases): less than 25°C
  2. Petrol (gasoline): 40-100°C
  3. Naphtha: 90-150°C
  4. Kerosene: 150-240°C
  5. Diesel: 220-300°C
  6. Fuel oil: 250-320ºC
  7. Lubricating oil: 300-350ºC
  8. Bitumen: >350°C
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30
Q

List five petroleum fractions used as fuels.

A
  1. LPG (refinery gases): fuels for taxis
  2. Petrol: fuels for private cars / vehicles
  3. Kerosene: fuels for aeroplanes
  4. Diesel: fuels for heavy vehicles like lorries and buses
  5. Fuel oil: fuels for ships and power plants
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31
Q

Petroleum fractions having large molecular sizes are cheaper. Why do aeroplanes use kerosene instead of fractions with larger molecular sizes as fuels?

A

The fractions with larger sizes produce sootier flame when burnt; the soot released may block and damage the aeroplane engine, therefore aeroplanes use kerosene as fuel.

32
Q

What are the usages of naphtha?

A

It is used as raw materials for production of Town Gas, plastics and other chemicals.

33
Q

What are the usages of kerosene?

A

It is used as aeroplane fuels, solvents, and as heating oil.

34
Q

What are the usages of lubricating oil?

A

It is used as lubricants to reduce friction, reduce corrosion, and is used to make waxes for cars.

35
Q

What are the usages of bitumen?

A

It is a material for covering road surfaces and roofs. It is waterproof, and prevents skidding of vehicles in rainy days.

36
Q

How does complete combustion of coal happen?

A

Complete combustion of coal happens when coal burns completely in a plentiful supply of oxygen. Its carbon is oxidised to carbon dioxide.

37
Q

What are the products of complete combustion?

A

Carbon dioxide and water only.

38
Q

What are the products of incomplete combustion?

A

Carbon dioxide, water, and/or carbon monoxide and carbon soot.

39
Q

How does combustion change the energy level of the reactants?

A

Energy is released to the surroundings as heat in combustion; it is an exothermic reaction.

40
Q

What is the chemical equation for the complete combustion of hexane?

A

C6H14 + 9½O2 -> 6CO2 + 7H2O

41
Q

Hexane undergoes incomplete combustion and produces carbon dioxide, carbon monoxide, and carbon soot in the molar ratio of 3:2:1.
What is the chemical equation of the reaction?

A

C6H14 + 7½O2 -> 3CO2 + 2CO + C + 7H2O

42
Q

Hexane undergoes incomplete combustion and produces carbon dioxide, carbon monoxide, and carbon soot in the molar ratio of 1:1:1.
What is the chemical equation of the reaction?

A

C6H14 + 6½O2 -> 2CO2 + 2CO + 2C + 7H2O

43
Q

Two samples of benzene are combusted. The first sample undergoes complete combustion. The second one undergoes incomplete combustion and produces carbon dioxide, carbon monoxide, and carbon soot in the molar ratio of 1:1:1.
What are the chemical equations of reaction? What is the difference between the amount of oxygen required for the two reactions?

A

Sample 1: C6H6 + 7½O2 -> 6CO2 + 3H2O
Sample 2: C6H6 + 4½O2 -> 2CO2 + 2CO + 2C + 3H2O
Incomplete combustion requires less oxygen per molecule of benzene.

44
Q

Why do hydrocarbons with larger molecular size burn with more orange and sooty flame?

A

The larger the molecular size, the more oxygen molecules are required for complete combustion. Therefore, there is a higher chance of incomplete combustion. Carbon soot is released from incomplete combustion, and the flame colour is due to the burning of carbon.

45
Q

How does an increased concentration of carbon dioxide in the atmosphere cause climate change?

A

As the concentration of carbon dioxide in the atmosphere increases, the greenhouse effect is enhanced, causing global warming which leads to climate change.

46
Q

What are greenhouse gases?

A

Greenhouse gases are gases which absorb infrared radiation emitted from the Earth and re-emit them in all directions, preventing infrared radiation from being re-radiated into space, thus trapping heat from the Sun in the atmosphere.

47
Q

List two sources of methane hydrate.

A

Under Arctic permafrost and beneath the ocean floor.

48
Q

Why is methane hydrate hard to extract?

A

It is a crystalline solid consisting of methane molecules surrounded by cages of interlocking water molecules. If it is warmed or pressurised, it will revert back into water and methane gas, but the release of methane gas could have a damaging impact on the environment.

49
Q

List 5 major types of air pollutants produced by burning fossil fuels.

A
  1. Suspended particulates (mainly carbon soot)
  2. Carbon monoxide
  3. Volatile compounds (unburnt hydrocarbons)
  4. Sulphur dioxide
  5. Nitrogen oxides
50
Q

How are suspended particulates produced in the process of burning fossil fuels?

A

Small carbon particles are produced during the incomplete combustion of fuels that contain carbon. Some diesel-powered vehicles with poor maintenance may release them as black smoke.

51
Q

What are the harmful effects of suspended particulates?

A

They can be breathed into the lungs to cause breathing problems and worsen asthma. They also reduce visibility.

52
Q

What are the solutions to suspended particulate pollution?

A

Install electrostatic precipitators in power plants, install particulate reduction devices in motor vehicles, or use a better fuel with lower chance of incomplete combustion.

53
Q

How is carbon monoxide produced in the process of burning fossil fuels?

A

Carbon monoxide is a product of incomplete combustion of fossil fuels.

54
Q

What are the harmful effects of carbon monoxide?

A

It is a poisonous gas.

55
Q

What are the solutions to carbon monoxide pollution?

A

Use a catalytic convertor or use a better fuel with lower chance of incomplete combustion.

56
Q

How are volatile organic compounds produced in the process of burning fossil fuels?

A

They are released as unburnt fuels from petrol engines.

57
Q

What are the harmful effects of volatile hydrocarbons in air?

A

Some hydrocarbons are carcinogenic.

58
Q

What are the solutions to volatile organic compound pollution?

A

Use a catalytic convertor or use a better fuel.

59
Q

How is sulphur dioxide produced in the process of burning fossil fuels?

A

They are released when fuels containing sulphur are burnt.

60
Q

What are the harmful effects of sulphur dioxide pollution?

A

It irritates the eyes and throat, causes breathing problems, and forms acid rain.

61
Q

What are the solutions to sulphur dioxide pollution?

A

Use flue gas desulphurisation plants or scrubbers in power plants, and use fuels with ultra low sulphur content.

62
Q

How are nitrogen oxides produced in the process of burning fossil fuels?

A

They are produced from the reaction between nitrogen and oxygen in the combustion engine in power plants and vehicles, which is very hot.

63
Q

What are the harmful effects of nitrogen oxides pollution?

A

They can cause breathing problems and worsen asthma. They cause acid rain and give photochemical smog with unburnt hydrocarbons.

64
Q

What are the solutions to nitrogen oxides pollution?

A

Install low nitrogen oxide burners in power plants, and install catalytic convertors in exhaust systems of motor vehicles.

65
Q

List 4 measures the Hong Kong Government has implemented to reduce air pollutant emissions from vehicles.

A
  1. An incentive programme is set up to replace diesel taxis / light buses with liquefied petroleum gas vehicles.
  2. A higher fuel and vehicle emission standard was adopted.
  3. An incentive programme is set up to retrofit old diesel vehicles with particulate reduction devices.
  4. The first registration tax for environmentally friendly vehicles are reduced.
66
Q

What is the working principle of flue gas desulphurisation plants and scrubbers?

A

They use calcium oxide or calcium hydroxide to absorb sulphur dioxide, producing insoluble calcium sulphite.

67
Q

What is the working principle of electrostatic precipitators?

A

They are installed in the chimneys, inducing charges on suspended particulates and making them stick onto the negative plate.

68
Q

Which pollutants can catalytic converters reduce?

A

Catalytic converters reduce the amounts of carbon monoxide, unburnt hydrocarbons, and nitrogen monoxide by converting them into less harmful substances.

69
Q

List 3 catalysts in the catalytic convertor.

A

Rhodium, palladium, platinum

70
Q

What is the internal structure of the catalytic convertor and the advantage?

A

The metals are spread thinly over a ceramic honeycomb-shaped support to provide a large surface area for reactions. This increases the rate of conversion while minimising the amount of expensive catalytic metals used.

71
Q

What is the chemical equation for the conversion of carbon monoxide in a catalytic convertor?

A

2CO + O2 -> 2CO2

72
Q

What is the chemical equation for the conversion of unburnt heptane in a catalytic convertor?

A

C7H16 + 11O2 -> 7CO2 + 8H2O

73
Q

What is the chemical equation for the conversion of nitrogen monoxide and carbon monoxide in a catalytic convertor?

A

2NO + 2CO -> N2 + 2CO2

74
Q

List 4 benefits of using fossil fuels.

A
  1. They are readily available at a relatively cheap price.
  2. They are efficient and can generate a lot of energy.
  3. They are easy and safe to transport.
  4. Fossil-fuel related industries generate job opportunities.
75
Q

List 6 risks of using fossil fuels.

A
  1. Burning fossil fuels releases carbon dioxide, which increases the greenhouse effect and contributes to global warming.
  2. Burning fossil fuels produce sulphur dioxide and nitrogen oxides, which contribute to acid rain.
  3. Exploration and mining of fossil fuels harm the environment.
  4. Coal mining is very dangerous.
  5. The extraction and transportation of fossil fuels require energy, increasing fossil fuel consumption.
  6. Petroleum leaks cause pollution and harm local wildlife.

HKDSE Chemistry (28 decks)

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