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chemistry > R1.3 - energy from fuels > Flashcards

R1.3 - energy from fuels Flashcards

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1
Q

What is combustion?

A

Reaction in which an element or compound burns on oxygen.

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2
Q

What does combustion produce?

A

Carbon dioxide and water

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3
Q

What does combustion of organic compounds do?

A

Combustion of organic compounds breaks the carbon chain.

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4
Q

What is made during incomplete combustion?

A

Carbon, Carbon monoxide and Water

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5
Q

Why is incomplete combustion dangerous?

A

Produces CO, which is toxic to humans as it affects oxygen uptake in our body, preventing oxygen from being carried around the body.

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6
Q

What is an ideal fuel?

A

A fuel that releases significant amounts of energy at a reasonable rate with minimal amounts of pollution.

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7
Q

What are fossil fuels and how are they formed?

A

Non-renewable sources of energy, such as crude oil and natural gas that are formed from the reduction of biological compounds.

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8
Q

What is crude oil and how is it formed?

A

A valuable fuel and chemical feedstock that is a mixture of alkanes, cyclo-alkanes that have been formed from the remains of marine animals subject to high pressure and temperature, causing the bacteria to decay the organic matter.

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9
Q

What are the advantages and disadvantages of crude oil?

A

Advantages:
- Easily transportable
- Volatile
- High enthalpy density
- Impurities removable
Disadvantages:
- Photochemical smog
- Carbon monoxide
- Acid rain
- Contributes to global warming

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10
Q

What is natural gas and how is it formed?

A

Mainly methane and nirtogen capped by impermeable rock and subject to high heat and pressure with bacteria decaying organic matter.
- Natural gas is explosive in air.

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11
Q

What are the advantages and disadvantages of natural gas?

A

Advantages:
- Cleanest fossil fuel
- Easily transportable
- No acid rain
- Low carbon content
- High specific energy
Disadvantages:
- Limited supply
- Risk of explosion
- Contributes to global warming

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12
Q

What is coal and how is it formed?

A

Most plentiful fossil fuel formed from the remains of plant life subject to geological heat and pressure, turning it into combustible sedimentary rock.

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13
Q

What are the advantages and disadvantages of coal?

A

Advantages:
- Cheap
- Safer than nuclear
- Ash used in roads
- Longest life span
- Easy to use
Disadvantages:
- Acid rain
- Contributes to global warming
- Particulates
- Mining is hard

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14
Q

What is a carbon footprint?

A

Measure of all the greenhouse gases we individually produce in our day to day activities through the use of fossil fuels.

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15
Q

What is the relationship between carbon content and specific energy?

A

Higher carbon content - more CO2 released and less energy released.
Lower carbon content - less CO2 released and more energy released.

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16
Q

How does carbon content link to combustion?

A

Lower carbon content - complete combustion
Higher carbon content - incomplete combustion

17
Q

What are the impacts of the greenhouse effect?

A
  • Rising sea levels
  • Melting ice caps
  • Extreme weather
  • Extinction of species
  • Loss of biodiversity
18
Q

What is the greenhouse effect?

A

Greenhouse gases allow short-wave radiation to pass through the atmosphere, but absorbs long-wave IR, which is re-emitted back into out atmosphere, warming it up.

19
Q

What is a biofuel and how is it formed?

A

Fuels that have formed from the biological fixation of carbon over a period of time through photosynthesis.

20
Q

What is photosynthesis?

A

6CO2 (g) + 6H2O (l) –> C6H12O6 (s) + 6O2 (g)
- An endothermic process which turns light energy into chemical energy.

21
Q

What are the disadvantages of photosynthesis?

A

Not an efficient process as only 10% of solar energy is captured.

22
Q

What is wood and how can it be used?

A

Wood is mainly made out of cellulose ( a polymer made out of glucose molecules).
- It has a higher O% and a lower C%, leading to a lower specific energy than coal.
- Water vapor and oxygen are lost when exposed to high pressures.

23
Q

What is ethanol and how can it be used?

A

Liquid biofuel made from the fermentation of plants high in sugar and starch at 37 degrees, in anaerobic conditions.
- Lower specific energy than octane as C-O and O-H bonds are already present.

24
Q

What is methane and how can it be used?

A

Produced by the bacterial breakdown of plant matter, producing carbon dioxide.
C6H12O6 (s) –> 3CO2 (g) + 3CH4 (g) = 50% of methane in carbohydrates
2C15H31COOH (s) + 14H2O (l) –> 9CO2 (g) + 23CH4 (g) = 72% methane in fats

25
Q

What are the advantages of biofuels?

A
  • Cheap
  • Readily available
  • Renewable and sustainable
  • Produces less pollution
26
Q

What are the disadvantages of biofuels?

A
  • Uses lots of land
  • High transport costs
  • Uses lots of fertilizers
  • Lower specific energy
27
Q

What is a fuel cell?

A

Used to convert chemical energy from a fuel directly into electrical energy.

28
Q

How does a hydrogen fuel cell work?

A

1) H2 goes into the cathode and donates electrons.
2) O2 goes into the anode and gains the electrons.
3) Water comes out of the bottom.
- Works with an alkaline electrolyte.

29
Q

What happens at the anode of a hydrogen fuel cell?

A

Hydrogen is oxidised in the presence of OH- ions to form water and electrons.
H2 (g) + 2OH- (aq) –> 2H2O (l) + 2e-

30
Q

What happens at the cathode of a hydrogen fuel cell?

A

Oxygen is reduced by gaining the electrons and reacting it with water to form OH- ions.
O2 (g) + 4e- + 2H2O (l) –> 4OH- (aq)

31
Q

What is the overall equation of a hydrogen fuel cell?

A

2H2 (g) + O2 (g) –> 2H2O (l)

32
Q

How can methanol be used in a fuel cell?

A

Methanol is oxidized using catalysts in a fuel cell to form CO2 and water is consumer at the anode and produced at the cathode.
CH3OH (g) + 1.5O2 (g) –> CO2 (g) + 2H2O (l)

33
Q

What are the half equations for a methanol fuel cell?

A

Methanol is oxidized at the anode:
CH3OH (l) + H2O (l) –> CO2 (g) + 6e- + 6H+ (aq)
Oxygen is reduced at the cathode:
O2 (g) + 4e- + 4H+ (aq) –> 2H2O (l)

34
Q

What is the full equation for the methanol fuel cell?

A

CH2OH (l) + H2O (l) –> CO2 (g) + 6H+ (aq) = 6e-

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