R1.3 - energy from fuels Flashcards
What is combustion?
Reaction in which an element or compound burns on oxygen.
What does combustion produce?
Carbon dioxide and water
What does combustion of organic compounds do?
Combustion of organic compounds breaks the carbon chain.
What is made during incomplete combustion?
Carbon, Carbon monoxide and Water
Why is incomplete combustion dangerous?
Produces CO, which is toxic to humans as it affects oxygen uptake in our body, preventing oxygen from being carried around the body.
What is an ideal fuel?
A fuel that releases significant amounts of energy at a reasonable rate with minimal amounts of pollution.
What are fossil fuels and how are they formed?
Non-renewable sources of energy, such as crude oil and natural gas that are formed from the reduction of biological compounds.
What is crude oil and how is it formed?
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.
What are the advantages and disadvantages of crude oil?
Advantages:
- Easily transportable
- Volatile
- High enthalpy density
- Impurities removable
Disadvantages:
- Photochemical smog
- Carbon monoxide
- Acid rain
- Contributes to global warming
What is natural gas and how is it formed?
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.
What are the advantages and disadvantages of natural gas?
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
What is coal and how is it formed?
Most plentiful fossil fuel formed from the remains of plant life subject to geological heat and pressure, turning it into combustible sedimentary rock.
What are the advantages and disadvantages of coal?
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
What is a carbon footprint?
Measure of all the greenhouse gases we individually produce in our day to day activities through the use of fossil fuels.
What is the relationship between carbon content and specific energy?
Higher carbon content - more CO2 released and less energy released.
Lower carbon content - less CO2 released and more energy released.
How does carbon content link to combustion?
Lower carbon content - complete combustion
Higher carbon content - incomplete combustion
What are the impacts of the greenhouse effect?
- Rising sea levels
- Melting ice caps
- Extreme weather
- Extinction of species
- Loss of biodiversity
What is the greenhouse effect?
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.
What is a biofuel and how is it formed?
Fuels that have formed from the biological fixation of carbon over a period of time through photosynthesis.
What is photosynthesis?
6CO2 (g) + 6H2O (l) –> C6H12O6 (s) + 6O2 (g)
- An endothermic process which turns light energy into chemical energy.
What are the disadvantages of photosynthesis?
Not an efficient process as only 10% of solar energy is captured.
What is wood and how can it be used?
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.
What is ethanol and how can it be used?
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.
What is methane and how can it be used?
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
What are the advantages of biofuels?
- Cheap
- Readily available
- Renewable and sustainable
- Produces less pollution
What are the disadvantages of biofuels?
- Uses lots of land
- High transport costs
- Uses lots of fertilizers
- Lower specific energy
What is a fuel cell?
Used to convert chemical energy from a fuel directly into electrical energy.
How does a hydrogen fuel cell work?
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.
What happens at the anode of a hydrogen fuel cell?
Hydrogen is oxidised in the presence of OH- ions to form water and electrons.
H2 (g) + 2OH- (aq) –> 2H2O (l) + 2e-
What happens at the cathode of a hydrogen fuel cell?
Oxygen is reduced by gaining the electrons and reacting it with water to form OH- ions.
O2 (g) + 4e- + 2H2O (l) –> 4OH- (aq)
What is the overall equation of a hydrogen fuel cell?
2H2 (g) + O2 (g) –> 2H2O (l)
How can methanol be used in a fuel cell?
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)
What are the half equations for a methanol fuel cell?
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)
What is the full equation for the methanol fuel cell?
CH2OH (l) + H2O (l) –> CO2 (g) + 6H+ (aq) = 6e-
