IB Chemistry home > Syllabus 2016 > Option C

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.

Nature of science:
Use theories to explain natural phenomena—energy changes in the world around us result from potential and kinetic energy changes at the molecular level.
Energy has both quantity and quality. (2.2)

• A useful energy source releases energy at a reasonable rate and produces minimal pollution.
• The quality of energy is degraded as heat is transferred to the surroundings.
Energy and materials go from a concentrated into a dispersed form. The quantity of the energy available for doing work decreases.
• Renewable energy sources are naturally replenished. Non-renewable energy sources are finite.
• Energy density = energy released from fuel/ volume of fuel consumed.
• Specific energy = energy released from fuel/ mass of fuel consumed.
• The efficiency of an energy transfer = useful output energy/total input energy x 100%.

Applications and skills:
• Discussion of the use of different sources of renewable and non-renewable energy.
• Determination of the energy density and specific energy of a fuel from the enthalpies of combustion, densities and the molar mass of fuel.
• Discussion of how the choice of fuel is influenced by its energy density or specific energy.

• The International Energy Agency is an autonomous organization based in Paris which works to ensure reliable, affordable and clean energy for its 28 member countries and beyond.
• The International Renewable Energy Agency (IRENA), based in Abu Dhabi, UAE, was founded in 2009 to promote increased adoption and sustainable use of renewable energy sources (bio-energy, geothermal energy, hydropower, ocean, solar and wind energy).

Theory of knowledge:
• “I have no doubt that we will be successful in harnessing the sun’s energy. If sunbeams were weapons of war we would have had solar energy centuries ago.” (Lord George Porter). In what ways might social, political, cultural and religious factors affect the types of research that are financed and undertaken, or rejected?
• There are many ethical issues raised by energy generation and its consequent contributions to pollution and climate change. What is the influence of political pressure on different areas of knowledge?

Syllabus and cross-curricular links:
Topic 5.1—enthalpies of combustion
Topic 10.2—the combustion of hydrocarbons
Environmental systems and societies topics—3.2, 3.3, 3.5 and 3.6
Physics topic 8.1—energy density
• Determination of the efficiency of an energy transfer process from appropriate data.
• Discussion of the advantages and disadvantages of the different energy sources in C.2 through to C.8.

• Aim 1: Discussions of the possible energy sources provide opportunities for scientific study and creativity within a global context.
• Aim 6: The energy density of different fuels could be investigated experimentally.
• Aim 7: Databases of energy statistics on a global and national scale can be explored here.
• Aim 8: Energy production has global economic and environmental dimensions.
The choices made in this area have moral and ethical implications.

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.

Nature of science:
Scientific community and collaboration—the use of fossil fuels has had a key role in the development of science and technology. (4.1)

• Fossil fuels were formed by the reduction of biological compounds that contain carbon, hydrogen, nitrogen, sulfur and oxygen.
• Petroleum is a complex mixture of hydrocarbons that can be split into different component parts called fractions by fractional distillation.
• Crude oil needs to be refined before use. The different fractions are separated by a physical process in fractional distillation.
• The tendency of a fuel to auto-ignite, which leads to “knocking” in a car engine, is related to molecular structure and measured by the octane number.
• The performance of hydrocarbons as fuels is improved by the cracking and catalytic reforming reactions.
• Coal gasification and liquefaction are chemical processes that convert coal to gaseous and liquid hydrocarbons.
• A carbon footprint is the total amount of greenhouse gases produced during human activities. It is generally expressed in equivalent tons of carbon dioxide.

Applications and skills:
• Discussion of the effect of chain length and chain branching on the octane number.
• Discussion of the reforming and cracking reactions of hydrocarbons and explanation how these processes improve the octane number.
• Deduction of equations for cracking and reforming reactions, coal gasification and liquefaction.
• Discussion of the advantages and disadvantages of the different fossil fuels.
• Identification of the various fractions of petroleum, their relative volatility and their uses.
• Calculations of the carbon dioxide added to the atmosphere, when different fuels burn and determination of carbon footprints for different activities.

• The cost of production and availability (reserves) of fossil fuels and their impact on the environment should be considered.

• The choice of fossil fuel used by different countries depends on availability, and economic, societal, environmental and technological factors.
• Different fuel rating systems (RON, MON or PON) are used in different countries.
• Ocean drilling, oil pipelines and oil spills are issues that demand international cooperation and agreement.

Syllabus and cross-curricular links:
Topics 5.1 and 5.3—enthalpy changes of combustion
Topics 10.1 and 20.3—hydrocarbons and isomerism
Topic 10.2 and option C.5—global warming
Option C.8—solar cells
Biology topic 4.3—carbon cycling

• Aim 6: Possible experiments include fractional distillation and catalytic cracking reactions.
• Aim 7: Databases of energy statistics on a global and national scale can be explored here.
• Aim 7: Many online calculators are available to calculate carbon footprints.
• Aim 8: Consideration of the advantages and disadvantages of fossil fuels illustrates the economic and environmental implications of using science and technology.

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.

Nature of science:
Assessing the ethics of scientific research—widespread use of nuclear fission for energy production would lead to a reduction in greenhouse gas emissions. Nuclear fission is the process taking place in the atomic bomb and nuclear fusion that in the hydrogen bomb. (4.5)

Nuclear fusion
• Light nuclei can undergo fusion reactions as this increases the binding energy per nucleon.
• Fusion reactions are a promising energy source as the fuel is inexpensive and abundant, and no radioactive waste is produced.
• Absorption spectra are used to analyse the composition of stars.
Nuclear fission
• Heavy nuclei can undergo fission reactions as this increases the binding energy per nucleon.
• 235U undergoes a fission chain reaction:

235U92 + 1n0 → 236U92 → X + Y + neutrons.

• The critical mass is the mass of fuel needed for the reaction to be self-sustaining.
• 239Pu, used as a fuel in “breeder reactors”, is produced from 238U by neutron capture.
• Radioactive waste may contain isotopes with long and short half-lives.
• Half-life is the time it takes for half the number of atoms to decay.

Applications and skills:
Nuclear fusion
• Construction of nuclear equations for fusion reactions.
• Explanation of fusion reactions in terms of binding energy per nucleon.
• Explanation of the atomic absorption spectra of hydrogen and helium, including the relationships between the lines and electron transitions.
Nuclear fission
• Deduction of nuclear equations for fission reactions.
• Explanation of fission reactions in terms of binding energy per nucleon.
• Discussion of the storage and disposal of nuclear waste.
• Solution of radioactive decay problems involving integral numbers of half-lives.

• Students are not expected to recall specific fission reactions.
• The workings of a nuclear power plant are not required.
• Safety and risk issues include: health, problems associated with nuclear waste and core meltdown, and the possibility that nuclear fuels may be used in nuclear weapons.
• The equations, are given in section 1 of the data booklet.

• The use of nuclear energy is monitored internationally by the International Atomic Energy Agency.
• High-energy particle physics research involves international collaboration.
There are accelerator facilities at CERN, DESY, SLAC, Fermi lab and Brookhaven. Results are disseminated and shared by scientists in many countries.
• The ITER project is a collaboration between many countries and aims to
demonstrate that fusion is an energy source of the future.

Theory of knowledge:
• The use of nuclear energy carries risks as well as benefits. Who should ultimately be responsible for assessing these? How do we know what is best for society and the individual?

Syllabus and cross-curricular links:
Topic 2.1—isotopes
Topic 2.2—the emission spectrum of hydrogen
Physics topic 7.2—nuclear fusion

• Aim 7: Computer animations and simulations of radioactive decay, and nuclear fusion and fission reactions.
• Aim 8: Consideration of the environmental impact of nuclear energy illustrating the implications of using science and technology.

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.

Nature of science:
Public understanding—harnessing the sun’s energy is a current area of research and challenges still remain. However, consumers and energy companies are being encouraged to make use of solar energy as an alternative energy source. (5.2)

• Light can be absorbed by chlorophyll and other pigments with a conjugated electronic structure.
• Photosynthesis converts light energy into chemical energy:
6CO2 + 6H2O ’ C6H12O6 + 6O2
• Fermentation of glucose produces ethanol which can be used as a biofuel:
C6H12O6 ’ 2C2H5OH + 2CO2
• Energy content of vegetable oils is similar to that of diesel fuel but they are not used in internal combustion engines as they are too viscous.
• Trans-esterification between an ester and an alcohol with a strong acid or base catalyst produces a different ester:
• In the transesterification process, involving a reaction with an alcohol in the presence of a strong acid or base, the triglyceride vegetable oils are converted to a mixture mainly comprising of alkyl esters and glycerol, but with some fatty acids.
• Transesterification with ethanol or methanol produces oils with lower viscosity that can be used in diesel engines.

Applications and skills:
• Identification of features of the molecules that allow them to absorb visible light.
• Explanation of the reduced viscosity of esters produced with methanol and ethanol.
• Evaluation of the advantages and disadvantages of the use of biofuels.
• Deduction of equations for transesterification reactions.

• Only a conjugated system with alternating double bonds needs to be covered.

Theory of knowledge:
• The claims of “cold fusion” were dismissed as the results are not reproducible.
Is it always possible to obtain replicable results in the natural sciences? Are reproducible results possible in other areas of knowledge?

Syllabus and cross-curricular links:
Topic 5.3—bond enthalpies
Topic 20.1—mechanism of nuclear substitution reactions
Biology topic 2.9—photosynthesis

• Aim 2: The conversion of solar energy is important in a number of different technologies.
• Aim 6: Experiments could include those involving photosynthesis, fermentation and transesterification.
• Aim 8: Transesterification reactions, with waste cooking oil, could reduce waste and produce excellent biofuels.

C.5 Environmental impact—global 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.

Nature of science:
Transdisciplinary—the study of global warming encompasses a broad range of concepts and ideas and is transdisciplinary. (4.1)
Collaboration and significance of science explanations to the public—reports of the Intergovernmental Panel on Climate Change (IPCC). (5.2)
Correlation and cause and understanding of science—CO2 levels and Earth average temperature show clear correlation but wide variations in the surface temperature of the Earth have occurred frequently in the past. (2.8)


• 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.
• There is a heterogeneous equilibrium between concentration of atmospheric carbon dioxide and aqueous carbon dioxide in the oceans.
• Greenhouse gases absorb IR radiation as there is a change in dipole moment as the bonds in the molecule stretch and bend.
• Particulates such as smoke and dust cause global dimming as they reflect sunlight, as do clouds.

Applications and skills:

• Explanation of the molecular mechanisms by which greenhouse gases absorb infrared radiation.
• Discussion of the evidence for the relationship between the increased concentration of gases and global warming.
• Discussion of the sources, relative abundance and effects of different greenhouse gases.
• Discussion of the different approaches to the control of carbon dioxide emissions.

• Greenhouse gases to be considered are CH4, H2O and CO2.

• This issue involves the international community working together to research and reduce the effects of global warming. Such attempts include the Intergovernmental Panel on Climate Change (IPCC) and the Kyoto Protocol which was extended in Qatar.

Theory of knowledge:
• Some people question the reality of climate change, and question the motives of scientists who have “exaggerated” the problem. How do we assess the evidence collected and the models used to predict the impact of human activities?

Syllabus and cross-curricular links:
Topics 7.1 and 17.1—equilibrium systems
Topic 8.2—acid–base equilibria
Topic 11.3—infrared spectra
Topic 13.2—transition metal complexes
Biology topic 4.4—climate change
Physics topic 8.1—thermal energy transfer

• Aim 6: The equilibrium between aqueous and gaseous carbon dioxide could be experimentally investigated.
• Discussion of pH changes in the ocean due to increased concentration of carbon dioxide in the atmosphere.

• Aim 7: Computer modelling is a powerful tool by which knowledge can be gained about the greenhouse effect.
• Aim 8: Discussions of climate change and green chemistry raise awareness of
the ethical, economic and environmental implications of using science and technology.

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.

Nature of science:
Environmental problems—redox reactions can be used as a source of electricity but disposal of batteries has environmental consequences. (4.8)

• 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.
• The voltage of a battery depends primarily on the nature of the materials used while the total work that can be obtained from it depends on their quantity.
• In a primary cell the electrochemical reaction is not reversible. Rechargeable cells involve redox reactions that can be reversed using electricity.
• A fuel cell can be used to convert chemical energy, contained in a fuel that is consumed, directly to electrical energy.
• Microbial fuel cells (MFCs) are a possible sustainable energy source using different carbohydrates or substrates present in waste waters as the fuel.
• The Nernst equation, can be used to calculate the potential of a half-cell in an electrochemical cell, under non-standard conditions.
• The electrodes in a concentration cell are the same but the concentration of the electrolyte solutions at the cathode and anode are different.

Applications and skills:
• Distinction between fuel cells and primary cells.
• Deduction of half equations for the electrode reactions in a fuel cell.
• Comparison between fuel cells and rechargeable batteries.
• Discussion of the advantages of different types of cells in terms of size, mass and voltage.
• Solution of problems using the Nernst equation.
• Calculation of the thermodynamic efficiency (ΔGH) of a fuel cell.
• Explanation of the workings of rechargeable and fuel cells including diagrams and relevant half-equations.

• A battery should be considered as a portable electrochemical source made up of one or more voltaic (galvanic) cells connected in series.
• The Nernst equation is given in the data booklet in section 1.
• 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.
• The Geobacter species of bacteria, for example, can be used in some cells to oxidize the ethanoate ions (CH3COO-) under anaerobic conditions.
• 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.

• Are battery recycling programmes equivalent in different areas of the globe?

Theory of knowledge:
• Does scientific language and vocabulary have primarily a descriptive or an interpretative function? Are the terms “electric current” and “internal resistance” accurate descriptions of reality or metaphors?

Syllabus and cross-curricular links:
Topic 9.1—redox reactions
Topic 19.1—electrochemical cells
Biology topic 6.5—muscle and nerve cells discussed in biology are concentration cells
Physics topic 5.3—the relationship between electrical power, voltage, resistance and current

• Aim 2: The conversion of chemical energy to electricity is important in a number of different technologies.
• Aim 6: The factors that affect the voltage of a cell and the lead–acid battery could be investigated experimentally.
• Aim 8: Consideration of the advantages and disadvantages of the different energy sources shows the economic and environmental implications of using science and technology. The environmental aspects of fuel cells, especially with regard to methanol, could be discussed.
• Aim 8: Disposal of primary batteries and the chemicals they use can introduce land and water pollution problems. Appreciation of the environmental impact of cadmium and lead pollution.
• Aim 8: Bacterial fuel cells use substrates found in waste water as the fuel and so can be used to clean up the environment.

C.7 Nuclear fusion and nuclear fission

Essential idea: Large quantities of energy can be obtained from small quantities of matter.

Nature of science:
Trends and discrepancies—our understanding of nuclear processes came from both theoretical and experimental advances. Intermolecular forces in UF6 are anomalous and do not follow the normal trends. (3.1)

Nuclear fusion:
• The mass defect (Δm) is the difference between the mass of the nucleus and the sum of the masses of its individual nucleons.
• The nuclear binding energy (ΔE) is the energy required to separate a nucleus into protons and neutrons.
Nuclear fission:
• The energy produced in a fission reaction can be calculated from the mass difference between the products and reactants using the Einstein mass–energy equivalence relationship.
• The different isotopes of uranium in uranium hexafluoride can be separated, using diffusion or centrifugation causing fuel enrichment.
• The effusion rate of a gas is inversely proportional to the square root of the molar mass (Graham’s Law).
• Radioactive decay is kinetically a first order process with the half-life related tothe decay constant by the equation.
• 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 (O2-), and hydroxyl (HO·). These free radicals can initiate chain reactions that can damage DNA and enzymes in living cells.

Applications and skills:
Nuclear fusion:
• Calculation of the mass defect and binding energy of a nucleus.
• Application of the Einstein mass–energy equivalence relationship, E=mc2, to
determine the energy produced in a fusion reaction.
Nuclear fission:
• Application of the Einstein mass–energy equivalence relationship to determine the energy produced in a fission reaction.
• Discussion of the different properties of UO2 and UF6 in terms of bonding and
• Solution of problems involving radioactive half-life.
• 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.
• Students are not expected to recall specific fission reactions.
• The workings of a nuclear power plant are not required.
• Safety and risk issues include: health, problems associated with nuclear waste, and the possibility that nuclear fuels may be used in nuclear weapons.
• Graham’s law of effusion is given in the data booklet in section 1.
• Decay relationships are given in the data booklet in section 1.
• A binding energy curve is given in the data booklet in section 36.

• There are only a very small number of countries that have developed nuclear weapons and the International Atomic Energy Agency strives to limit the spread of this technology. There are disputes about whether some countries are developing nuclear energy for peaceful or non-peaceful purposes.
• Nuclear incidents have a global effect; the accidents at Three Mile Island and Chernobyl and the problems at Fukushima caused by a tsunami could be discussed to illustrate the potential dangers.

Theory of knowledge:
• “There is no likelihood that humans will ever tap the power of the atom.” (Robert Millikan, Nobel Laureate Physics 1923 quoted in 1928). How can the impact of new technologies be predicted? How reliable are these predictions?
How important are the opinions of experts in the search for knowledge?
• The release of energy during fission reactions can be used in times of peace to generate energy, but also can lead to destruction in time of war. Should scientists be held morally responsible for the applications of their discoveries?
Is there any area of scientific knowledge the pursuit of which is morally unacceptable?

Syllabus and cross-curricular links:
Topics 4.1 and 4.3—structure and bonding
Topic 16.1—first order reactions
Physics topic 7.2—nuclear fusion
Geography—the different polices and attitudes to nuclear energy are discussed in resources sections in the guide.

• Aim 7: Computer animations and simulations of radioactive decay, and nuclear
fusion and fission reactions.
• Aim 8: Consideration of the advantages and disadvantages of nuclear fusion illustrates the economic and environmental implications of using science and technology. The use of fusion reactions in the hydrogen bomb can also be discussed.

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).

Nature of science:
Transdisciplinary—a dye-sensitized solar cell, whose operation mimics photosynthesis and makes use of TiO2 nanoparticles, illustrates the transdisciplinary nature of science and the link between chemistry and biology. (4.1)
Funding—the level of funding and the source of the funding is crucial in decisions regarding the type of research to be conducted. The first voltaic cells were produced by NASA for space probes and were only later used on Earth. (4.7)

• Molecules with longer conjugated systems absorb light of longer wavelength.
• The electrical conductivity of a semiconductor increases with an increase in temperature whereas the conductivity of metals decreases.
• The conductivity of silicon can be increased by doping to produce n-type and p-type
• Solar energy can be converted to electricity in a photovoltaic cell.
• 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:
• Relation between the degree of conjugation in the molecular structure and the wavelength of the light absorbed.
• Explanation of the operation of the photovoltaic and dye-sensitized solar cell.
• Explanation of how nanoparticles increase the efficiency of DSSCs.
• Discussion of the advantages of the DSSC compared to the silicon-based photovoltaic cell.

• The relative conductivity of metals and semiconductors should be related to ionization energies.
• 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 3 element. In n-type semiconductors inclusion of a group 5 element provides extra electrons.
• 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.
• Specific redox and electrode reactions in the newer Grätzel DSSC should be covered. An example is the reduction of I2/I3─ ions to I─.

• The harnessing of solar energy could change the economic fortunes of countries with good supplies of sunlight and unused land.

Theory of knowledge:
• A conjugated system has some similarities with a violin string. How useful is this metaphor? What are the underlying reasons for these similarities? What role do models and metaphors play in the acquisition of knowledge?

Syllabus and cross-curricular links:
Topic 3.2—patterns in ionization energy
Topic 9.1—redox reactions
Biology topic 2.9—photosynthesis

• Aim 6: Students could build an inexpensive dye-sensitized solar cell and investigate their photovoltaic properties.
• Aim 7: The properties of DSSCs can be best investigated using data loggers.