HL Option C

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C.6 Primary and secondary cells

Understandings:
In a primary cell the electrochemical reaction is not reversible. Rechargeable cells involve redox reactions that can be reversed using electricity.
Applications:
Explanation of the workings of rechargeable and fuel cells including diagrams and relevant half-equations.
Guidance:
The lead–acid storage battery, the nickel–cadmium (NiCad) battery and the lithium–ion battery should be considered.
Students should be familiar with the anode and cathode half-equations and uses of the different cells.

C.6 Fuel cells

Understandings:
A fuel cell can be used to convert chemical energy, contained in a fuel that is consumed, directly to electrical energy.
Applications and skills:
Distinction between fuel cells and primary cells
Guidance:
Hydrogen and methanol should be considered as fuels for fuel cells. The operation of the cells under acid and alkaline conditions should be considered. Students should be familiar with proton-exchange membrane (PEM) fuel cells.

C.6 Efficiency of fuel cells

Applications and skills:
Calculation of the thermodynamic efficiency (ΔG/ΔH) of a fuel cell.

C.6 Microbial fuel cells

Understandings:
Microbial fuel cells (MFCs) are a possible sustainable energy source using different carbohydrates or substrates present in waste waters as the fuel.
Guidance:
The Geobacter species of bacteria, for example, can be used in some cells to oxidize the ethanoate ions (CH COO-) under anaerobic conditions.

C.6 The Nernst equation

Understandings:
The Nernst equation can be used to calculate the potential of a half-cell in an electrochemical cell under non-standard conditions.
Applications and skills:
Solution of problems using the Nernst equation.
Guidance:
The Nernst equation is given in the data booklet in section 1.

C.6 Concentration cells

Understandings:
The electrodes in a concentration cell are the same but the concentration of the electrolyte solutions at the cathode and anode are different.

C.7 Calculating mass defect

Understandings:
The mass defect (∆m) is the difference between the mass of the nucleus and the sum of the masses of its individual nucleons.
Applications and skills:
Calculation of the mass defect and binding energy of a nucleus.
Note there are two versions of this video, one uses more precise masses for the nuclei.

There is a slight mistake in the video: the mass of an electron should be 9.109383 x 10-31 kg.

C.7 Calculating binding energy

Understandings:
The nuclear binding energy (ΔE) is the energy required to separate a nucleus into protons and neutrons.
Applications and skills:
Calculation of the mass defect and binding energy of a nucleus.
Note there are two versions of this video, one uses more precise masses for the mass defect and the other gives the binding energy in kJ/nucleon.

C.7 Calculating the energy released in nuclear reactions

Understandings:
The energy produced in a nuclear reactions can be calculated from the mass difference between the products and reactants using the Einstein mass–energy equivalence relationship E=mc2
Applications and skills:
Application of the Einstein mass–energy equivalence relationship to determine the energy produced in nuclear reactions.

C.7 Rate of radioactive decay

Understandings:
Radioactive decay is kinetically a first order process with the half-life related to the decay constant by the equation t1/2 = ln2/lamda
Applications and skills:
Solution of problems involving radioactive half-life.
Guidance:
Decay relationships are given in the data booklet in section 1.

C.7 Graham's law of effusion

Understandings:
The effusion rate of a gas is inversely proportional to the square root of the molar mass (Graham’s Law).
Applications and skills:
Explanation of the relationship between Graham’s law of effusion and the kinetic theory.
Solution of problems on the relative rate of effusion using Graham’s law.

C.7 Uranium enrichment

Understandings:
The different isotopes of uranium in uranium hexafluoride can be separated, using diffusion or centrifugation causing fuel enrichment.
Applications and skills:
Discussion of the different properties of UO2 and UF6 in terms of bonding and structure.

C.7 Ionizing radiation

Understandings:
The dangers of nuclear energy are due to the ionizing nature of the radiation it produces which leads to the production of oxygen free radicals such as superoxide, and hydroxyl. These free radicals can initiate chain
reactions that can damage DNA and enzymes in living cells.

C.8 Conjugated systems

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.

C.8 Electrical conductivity of metals and semiconductors

Understanding:
The electrical conductivity of a semiconductor increases with an increase in temperature whereas the conductivity of metals decreases.
Guidance:
The relative conductivity of metals and semiconductors should be related to ionization energies.

C.8 n-type and p-type semiconductors

Understanding:
The conductivity of silicon can be increased by doping to produce n-type and p- type semiconductors.
Guidance:
Only a simple treatment of the operation of the cells is needed. In p-type semiconductors, electron holes in the crystal are created by introducing a small percentage of a group 13 element. In n-type semiconductors inclusion of a group 15 element provides extra electrons.

C.8 Photovoltaic cells

Understandings:
Solar energy can be converted to electricity in a photovoltaic cell.
Guidance:
In a photovoltaic cell the light is absorbed and the charges separated in the silicon semiconductor.

C.8 Dye-sensitized solar cells (DSSCs)

Understandings:
DSSCs imitate the way in which plants harness solar energy. Electrons are "injected" from an excited molecule directly into the TiO2 semiconductor.
The use of nanoparticles coated with light-absorbing dye increases the effective surface area and allows more light over a wider range of the visible spectrum to be absorbed.
Applications and skills:
Explanation of the operation of the dye-sensitized solar cell.
Explanation of how nanoparticles increase the efficiency of DSSCs.

C.8 DSSCs vs silicon-based PV cells

Applications and skills:
Discussion of the advantages of the DSSC compared to silicon-based PV cells.
Guidance:
In a photovoltaic cell the light is absorbed and the charges separated in the silicon semiconductor. The processes of absorption and charge separation are separated in a dye-sensitized solar cell.