Photosynthesis and respiration are important processes in the cycling of carbon and oxygen on Earth.
In photosynthesis the light energy absorbed by chlorophyll is stored as chemical energy in carbohydrates such as glucose.
- Describe and write the equation for photosynthesis.
The chemical energy present in carbohydrates can be accessed by respiration and combustion.
- Describe and write the equation for the aerobic respiration of glucose.
Fossil fuels (coal, petroleum, and natural gas) have been formed over geological time scales by anaerobic decomposition of dead organisms. They are considered to be non-renewable because reserves are depleted more quickly than they are formed.
Carbon-based fuels provide energy and are feedstock for the chemical industry.
- Discuss the advantages and disadvantages of using carbon-based fuels as sources of heat energy, compared with their use as feedstock.
Video: Fossil fuels
Renewable energy is generated over time scales of years to decades, from sources that are replenished much more quickly than fossil fuels.
- Identify bioethanol, biodiesel, sunlight, and wind as renewable energy sources.
- Compare the contributions of fossil fuels to global warming with those from renewable energy sources.
Videos: Renewable Fuels | Pros and Cons
Biofuels are produced by present-day biological processes.
- Identify bioethanol and biodiesel as biofuels.
- Describe the production, from biological materials, of ethanol and biodiesel, including the writing of chemical equations for the reactions involved.
- Explain how fossil fuels contribute more than biofuels to global warming.
Videos: Biofuels from Plants and Algae | Fuels for the Future
The complete combustion of fuels containing carbon and hydrogen produces carbon dioxide and water and energy.
- Write thermochemical equations for the complete combustion of fuels in which the only products are carbon dioxide and water.
Video: Combustion
Incomplete combustion, producing carbon (soot) and carbon monoxide, is more likely with longer-chain carbon-based fuels.
- Explain why incomplete combustion is more likely with longer-chain carbon-based fuels than with shorter chains.
- Discuss the undesirable consequences of incomplete combustion.
Video: Flippin' Science
The energy released in combustion of fuels can be determined experimentally.
- Use experimental data to determine the enthalpy of combustion of a fuel.
- Undertake thermochemical calculations involving enthalpy changes and temperature changes of a specified mass of water given the necessary data.
Videos: The Energy of Chemical Reactions | Flippin' Science
Practice: Energy calculations
Fuels, including fossil fuels and biofuels, can be compared in terms of their energy output and the nature of products of combustion.
- Calculate the quantities of heat evolved per mole, per gram, and per litre (for liquids) for the complete combustion of fuels.
- Compare fuels given appropriate data.
Although most electricity is generated using fuels to drive steam turbines, electrical energy can be also be generated using photovoltaic cells (known as solar cells) and directly from oxidation of fuels using galvanic cells.
- Explain the advantages and disadvantages of direct electricity generation (photovoltaic and fuel cells) compared to using steam turbines.
Notes: Advantages and disadvantages
Video: Fuels for the Future (or long equivalent)
Fuel cells, including flow cells, are galvanic cells in which the electrode reactants are available in continuous supply.
- State the advantages and disadvantages of fuel cells compared with other galvanic cells.
- Identify the anode and cathode and their charges, as well as the direction of ion and electron flow, in a fuel cell, given sufficient information.
- Write electrode half-equations for a fuel cell given sufficient information.
- Discuss the advantages of flow cells compared with other fuel cells.
Notes: Advantages and disadvantages
Animated Notes: Galvanic Cells (revision)
Animated Notes: Fuel Cells
Video: Flippin' Science
Practice program: Half equation method practice
Hydrogen is a fuel that is produced from fossil fuels, biomass, or water.
• Compare the benefits of producing hydrogen from each of these three sources.
• Describe the benefits of using hydrogen, rather than fossil fuels, as a fuel.