Option C - Energy
C.1 Energy sources - core
Essential idea: Societies are completely dependent on energy resources. The quantity of energy is conserved in any conversion but the quality is degraded.
Understandings A useful energy source releases energy at a reasonable rate and produces minimal pollution. Applications and skills Discussion of the use of different sources of renewable and non-renewable energy. |
C.2 Fossil fuels
Essential idea: The energy of fossil fuels originates from solar energy which has been stored by chemical processes over time. These abundant resources are nonrenewable but provide large amounts of energy due to the nature of chemical bonds in hydrocarbons.
Understandings Fossil fuels were formed by the reduction of biological compounds that contain carbon, hydrogen, nitrogen, sulfur and oxygen. Applications and skills Discussion of the effect of chain length and chain branching on the octane number. Guidance: The cost of production and availability (reserves) of fossil fuels and their impact on the environment should be considered. |
C.3 Nuclear fusion and fission
Essential idea: The fusion of hydrogen nuclei in the sun is the source of much of the energy needed for life on Earth. There are many technological challenges in replicating this process on Earth but it would offer a rich source of energy. Fission involves the splitting of a large unstable nucleus into smaller stable nuclei.
Understandings Nuclear fusion 235U92 + 1n0 ? 236U92 ? X + Y + neutrons. The critical mass is the mass of fuel needed for the reaction to be self-sustaining. Applications and skills Nuclear fusion Guidance: Students are not expected to recall specific fission reactions. |
C.4 Solar energy
Essential idea: Visible light can be absorbed by molecules that have a conjugated structure with an extended system of alternating single and multiple bonds. Solar energy can be converted to chemical energy in photosynthesis.
Understandings Light can be absorbed by chlorophyll and other pigments with a conjugated electronic structure. Applications and skills Identification of features of the molecules that allow them to absorb visible light. Guidance: Only a conjugated system with alternating double bonds needs to be covered. |
C.5 Environmental impactglobal warming
Essential idea: Gases in the atmosphere that are produced by human activities are changing the climate as they are upsetting the balance between radiation entering and leaving the atmosphere.
Understandings Greenhouse gases allow the passage of incoming solar short wavelength radiation but absorb the longer wavelength radiation from the Earth. Some of the absorbed radiation is re-radiated back to Earth. Applications and skills Explanation of the molecular mechanisms by which greenhouse gases absorb infrared radiation. Guidance: Greenhouse gases to be considered are CH4, H2O and CO2. |
C.6 Electrochemistry, rechargeable batteries and fuel cells - AHL
Essential idea: Chemical energy from redox reactions can be used as a portable source of electrical energy.
Understandings An electrochemical cell has internal resistance due to the finite time it takes for ions to diffuse. The maximum current of a cell is limited by its internal resistance. Applications and skills Distinction between fuel cells and primary cells. Guidance: A battery should be considered as a portable electrochemical source made up of one or more voltaic (galvanic) cells connected in series. |
C.7 Nuclear fusion and nuclear fission
Essential ideas: Large quantities of energy can be obtained from small quantities of matter.
Understandings Nuclear fusion: Applications and skills Nuclear fusion: Guidance: Students are not expected to recall specific fission reactions. |
C.8 Photovoltaic cells and dye-sensitized solar cells (DSSC)
Essential idea: When solar energy is converted to electrical energy the light must be absorbed and charges must be separated. In a photovoltaic cell both of these processes occur in the silicon semiconductor, whereas these processes occur in separate locations in a dye-sensitized solar cell (DSSC).
Understandings Molecules with longer conjugated systems absorb light of longer wavelength. Applications and skills Relation between the degree of conjugation in the molecular structure and the wavelength of the light absorbed. Guidance: The relative conductivity of metals and semiconductors should be related to ionization energies. |