R1.3Reactivity 1 — What drives chemical reactions?

Energy from fuels — IB Chemistry SL Revision Notes & Topical Questions

20 min read 33 parts Lesson 3 of 8 1 quiz

📚 IB Chemistry SL Hub / Topical Revision

0%read

Lesson summary

R1.3 Energy from fuels — IB CHEMISTRY SL notes: Write equations for complete and incomplete combustion, evaluate fossil fuels and biofuels, link CO2 to climate, calculate specific energy and describe fuel cells.Combustion — a rapid, exothermic oxidation of a fuel that needs oxyge…

Non-metals
Organic fuels
Conditions
Hydrocarbons
Carbon monoxide
Carbon content

Section 1 of 33Combustion reactions

Combustion

Combustion a rapid, exothermic oxidation of a fuel that needs oxygen and an ignition source, giving heat and light.

Metals

Metals all metals oxidise, but only reactive or finely divided ones combust, e.g. 2Mg + O₂ → 2MgO;
- copper only forms black CuO on heating.

Non-metals

Non-metals form covalent, usually acidic oxides, e.g. S + O₂ → SO₂ and P₄ + 5O₂ → P₄O₁₀.

Redox

Redox the fuel is oxidised and oxygen is reduced.

Organic fuels

Organic fuels hydrocarbons and alcohols are used because they release much energy,
- and their high activation energy makes them safe to store and transport.

Section 2 of 33Complete combustion

Conditions

Conditions a plentiful supply of oxygen, giving CO₂ and H₂O.

Hydrocarbons

C_xH_y + (x + y/4)O₂ → xCO₂ + (y/2)H₂O, e.g. CH₄ + 2O₂ → CO₂ + 2H₂O.

Alcohols

Alcohols e.g. C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O, where the oxygen in the alcohol must be counted.

Balancing

Balancing balance carbon, then hydrogen, then supply the product oxygen from O₂, using fractions and doubling if needed.

Flame

Flame a Bunsen burner gives a blue, non-luminous flame.

Section 3 of 33Incomplete combustion

Conditions

Conditions limited oxygen, common in car engines and faulty boilers, giving a yellow, luminous flame.

Products

Products water plus carbon monoxide and/or carbon (soot), and it releases less energy per mole than complete combustion.

Carbon monoxide

Carbon monoxide colourless, odourless and toxic because it binds irreversibly to haemoglobin and prevents oxygen transport, e.g. C₃H₈ + 3.5O₂ → 3CO + 4H₂O.

Soot

C₃H₈ + 2O₂ → 3C + 4H₂O, causing respiratory problems and global dimming.

Hydrogen

Hydrogen is never a product because it is preferentially oxidised to water.

Carbon content

Carbon content compounds with a higher percentage of carbon, such as benzene derivatives, burn with sootier flames.

Alcohols

Alcohols burn more cleanly than hydrocarbons because they already contain oxygen.

Section 4 of 33Fossil fuels

Origin
- coal, oil and natural gas formed over millions of years from dead organisms, so they are non-renewable and finite.

Fuel	Advantages	Disadvantages
Coal	Cheap, widely available, long-lasting, safe to store	Most CO₂ per unit energy, SO₂ and particulates, mining damage
Oil	High energy density, easily transported and refined by fractional distillation and cracking	CO₂, SO₂, CO and smog, oil spills, uneven distribution
Natural gas	Cheapest, high specific energy, burns cleanly with least CO₂	Hard and costly to store under pressure, leaks of methane

Chain length
- as hydrocarbon chains lengthen, more CO₂ and less energy per gram are released,
  - and incomplete combustion is more likely; methane releases the most energy per gram.

Section 5 of 33Specific energy and enthalpy of combustion

Heat energy

Heat energy q = mcΔT, with c = 4.18 J g⁻¹ K⁻¹ for water.

What the symbols mean: E, Q or q = energy transferred (J) · m = mass (kg; g in chemistry calorimetry) · c = specific heat capacity (J kg⁻¹ °C⁻¹; water 4.18 J g⁻¹ °C⁻¹) · ΔT or Δθ = temperature change (°C or K)

Enthalpy of combustion

ΔH_c = −q/n(fuel), in kJ mol⁻¹.

Specific energy

Specific energy the energy released per unit mass of fuel, equal to |ΔH_c| divided by molar mass in kg mol⁻¹ (kJ kg⁻¹).

Energy density

Energy density the energy released per unit volume of fuel (kJ dm⁻³), equal to specific energy × density.

Experimental method

Experimental method burn a fuel in a spirit burner under a copper calorimeter of water and find the fuel mass lost.

Low experimental value

Low experimental value the result is less exothermic than the data-booklet value because of heat loss, incomplete combustion, fuel evaporation and heat absorbed by the calorimeter.

Alcohols

Alcohols release less energy per gram than hydrocarbons because they are partly oxidised, so ethanol has lower specific energy than octane.

Section 6 of 33Carbon dioxide and the greenhouse effect

Carbon dioxide and the greenhouse effect

Sources

Sources burning fossil fuels, deforestation, livestock (methane) and decomposition of carbonates.
- (especially for electricity)

Greenhouse gases

CO₂, CH₄, N₂O/NO_x and water vapour.

Mechanism

Mechanism short-wavelength radiation from the Sun reaches the Earth,
which re-emits longer-wavelength infrared, and greenhouse gases absorb it because their bond vibrations change the dipole moment.

Re-radiation

Re-radiation the gases re-emit the energy in all directions, trapping heat.

Enhanced greenhouse effect

Enhanced greenhouse effect extra warming from human-made increases in greenhouse gas concentrations, causing global warming and climate change.

Oceans

Oceans dissolved CO₂ forms carbonic acid, causing ocean acidification.

Monitoring

Mauna Loa records CO₂ since 1958, with seasonal fluctuations caused by photosynthesis.

Section 7 of 33Biofuels

Renewable resources

Renewable resources replaced as fast as or faster than they are used; non-renewable ones are finite.

Bioethanol

Bioethanol glucose from photosynthesis is fermented anaerobically by yeast, C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂.

Biodiesel

Biodiesel triglycerides react with methanol by transesterification, usually with an alkali catalyst, to give methyl esters;
- excess methanol shifts the equilibrium.

Biogas

Biogas anaerobic breakdown of organic waste gives mostly CH₄ and CO₂.

Carbon neutrality

CO₂ absorbed in growth equals that released on burning, but energy used in farming, transport and processing adds CO₂.

Advantages	Disadvantages
Renewable and close to carbon neutral	Land used instead of food crops and deforestation
Can be made from organic waste, reducing landfill	Fertiliser and pesticide use and soil depletion
Create jobs and income	Lower specific energy than fossil fuels and costly engine conversion

Section 8 of 33Fuel cells

Definition

Definition an electrochemical cell that converts the chemical energy of a continuously supplied fuel and oxidant directly into electrical energy.

Operation

Operation the cell runs while fuel and oxygen are supplied, with no recharging, and energy is not stored in the cell.

Efficiency

Efficiency higher than combustion engines because chemical energy becomes electrical energy without passing through heat.

Cell	Anode	Cathode
Hydrogen, acidic (PEM)	H₂ → 2H⁺ + 2e⁻	O₂ + 4H⁺ + 4e⁻ → 2H₂O
Hydrogen, alkaline	H₂ + 2OH⁻ → 2H₂O + 2e⁻	O₂ + 2H₂O + 4e⁻ → 4OH⁻
Methanol (PEM)	CH₃OH + H₂O → CO₂ + 6H⁺ + 6e⁻	O₂ + 4H⁺ + 4e⁻ → 2H₂O

1Overall

Overall hydrogen cell 2H₂ + O₂ → 2H₂O (E = +1.23 V) and methanol cell 2CH₃OH + 3O₂ → 2CO₂ + 4H₂O.

2Hydrogen cell advantages

Hydrogen cell advantages water is the only product, no NO_x, quiet with no moving parts.

3Hydrogen cell disadvantages

Hydrogen cell disadvantages expensive platinum catalyst, flammable and hard-to-store hydrogen with low energy density by volume,
- and mostly made from fossil fuels.

4Methanol cell versus hydrogen

Methanol cell versus hydrogen easier to store, higher energy density by volume and can come from biomass,
- but toxic, flammable, lower power and it produces CO₂.

Section 9 of 33More from the specification

Carbon dioxide

A gas that turns limewater cloudy.

Chemical formula

Symbols and numbers showing the relative number of atoms of each element.

Section 10 of 33Combustion and reactivity with oxygen

Combustion

Combustion a type of oxidation in which a substance reacts with oxygen and releases energy.

Non-metals

Non-metals form non-metal oxides, e.g. sulfur + oxygen → sulfur dioxide.

Complete combustion

Complete combustion hydrocarbons and alcohols burning in plenty of oxygen give carbon dioxide and water.

Hydrocarbon pattern

C_xH_y + (x + y/4)O₂ → xCO₂ + (y/2)H₂O.

Incomplete combustion

Incomplete combustion limited oxygen gives carbon monoxide and/or carbon (soot) with water and a smaller energy release.

Carbon monoxide

Carbon monoxide is a toxic gas.

Section 11 of 33Balancing combustion equations

Balancing combustion equations

Balance carbon first, using one CO₂ for each carbon.

Balance hydrogen next, using one H₂O for each two hydrogens.

Count the oxygen atoms on the product side and supply them from O₂, using fractions and then doubling for whole numbers.

Butane

C₄H₁₀ + 6.5O₂ → 4CO₂ + 5H₂O, or 2C₄H₁₀ + 13O₂ → 8CO₂ + 10H₂O.

Ethanol

C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O, because the oxygen already in the alcohol counts.

Section 12 of 33Calculating the mass of carbon dioxide produced

What the symbols mean:

Calculate the moles of fuel, n = m/M.

What the symbols mean: n = amount of substance (mol) · m = mass (g) · M or M_r = molar mass (g mol⁻¹, numerically equal to M_r)

Use the mole ratio from the balanced equation, e.g. 1 C₄H₁₀ : 4 CO₂.

Multiply the moles of CO₂ by its molar mass, 12.01 + 2 × 16.00 = 44.01 g mol⁻¹.

Mole ratio

Mole ratio use the mole ratio, not the mass ratio.

Mass relationship

Mass relationship the mass of CO₂ formed exceeds the mass of fuel because oxygen from the air is added to the carbon, about 3 g of CO₂ per gram of a hydrocarbon such as butane.

Carbon content

Carbon content a fuel with a higher proportion of carbon produces more CO₂ per kilogram.

Section 13 of 33Using the energy released

Energy released

Energy released n × |ΔH_c|.

Fair comparison

Fair comparison compare energy per gram, per mole and CO₂ per kilojoule on the same basis.

Methane

Methane has the lowest CO₂ per unit energy among hydrocarbons because it has the highest hydrogen-to-carbon ratio.

Section 14 of 33Combustion of alcohols

Fuel use

Fuel use alcohols are used as fuels as well as hydrocarbons.

Enthalpy trend

Enthalpy trend the enthalpy of combustion rises with chain length by roughly 650 kJ mol⁻¹ for each extra CH₂ unit,
- because more bonds form in the products.

Energy per gram

Energy per gram alcohols release less energy per gram than hydrocarbons because they already contain oxygen.

Section 15 of 33Carbon dioxide and the greenhouse effect link

Greenhouse gas

CO₂ from combustion contributes to the greenhouse effect.

Sources

Sources electricity generation accounts for a large part of fossil fuel use.

Trend

Trend atmospheric CO₂ has risen steadily, with seasonal ups and downs caused by photosynthesis in the northern hemisphere.

Removal

Removal photosynthesis removes CO₂ from the air and the oceans dissolve some, forming carbonic acid.

Section 16 of 33More from the specification

Section 17 of 33Carbon dioxide formed by burning a fuel

Source of the amount

Source of the amount the balanced equation gives the moles of CO₂ from the moles of fuel.

Butane

C₄H₁₀ + 6.5O₂ → 4CO₂ + 5H₂O, so one mole of fuel gives four moles of CO₂.

Carbon dioxide formed by burning a fuel

Convert the mass of fuel to moles.

Use the 1 : 4 ratio to find the moles of CO₂.

Multiply by 44.01 g mol⁻¹ to get the mass.

Section 18 of 33Rising carbon dioxide and its sources

Trend

Trend atmospheric CO₂ has increased steadily because of human activity.

Main source

Main source burning fossil fuels for electricity, transport and industry.

Other sources

Other sources deforestation, livestock and cement production.
- (which also release methane)

Seasonal fluctuation

Seasonal fluctuation an annual cycle is superimposed on the rise because plants take in more CO₂ in the growing season.

Carbonate sources

CO₂ is released when carbonate rocks are heated (CaCO₃ → CaO + CO₂) and when acids react with carbonates to give a salt, water and CO₂.

Other natural sources

Other natural sources respiration of plants and animals.

Section 19 of 33Greenhouse gases

Carbon dioxide

Carbon dioxide from respiration and burning fuels.

Methane

Methane from livestock, landfills and mining.

Nitrogen oxides

Nitrogen oxides from impurities in fossil fuels and high-temperature combustion.

Water vapour

Water vapour from combustion and evaporation.

Importance

Importance without the natural greenhouse effect Earth's temperature would swing widely, as on Mars.
- (20 °C to −153 °C)

Section 20 of 33Mechanism of the greenhouse effect

The Sun emits mostly short-wavelength radiation (visible and ultraviolet) that passes through the atmosphere.

The Earth's surface absorbs it and re-emits longer-wavelength infrared radiation.

Greenhouse gases absorb part of this infrared radiation.

They re-emit the energy in all directions, so some returns to the surface and the lower atmosphere warms.

1Why gases absorb

Why gases absorb molecules absorb infrared when their bond vibrations change the dipole moment, so CO₂ and CH₄ absorb but N₂ and O₂ do not.

2Enhanced greenhouse effect

Enhanced greenhouse effect the extra warming caused by human-made increases in greenhouse gas concentrations.

Section 21 of 33Effects and responses

Climate

Climate a rise in global mean temperature, melting ice and rising sea levels.

Oceans

Oceans dissolved CO₂ forms carbonic acid, lowering pH and harming organisms with calcium carbonate shells.

Reduction strategies

Reduction strategies greater efficiency, renewable energy, carbon capture and storage, and replacing fossil fuels with biofuels or hydrogen.

Evaluation

Evaluation compare CO₂ emitted per kilojoule delivered and consider the whole life cycle, including production and transport.

Section 22 of 33Structuring answers on CO<sub>2</sub> and climate

Chain of reasoning

Chain of reasoning source of the gas, property that makes it a greenhouse gas, absorption and re-emission of infrared, then the consequence.

Solutions

Solutions name the strategy, say how it reduces net CO₂ and state one limitation such as cost or land use.

Quantitative pattern

Quantitative pattern moles of fuel, moles of CO₂ from the equation ratio, then mass or volume, showing the molar masses used.

Section 23 of 33More from the specification

1Coordination chemistry of d-block metals

Coordination chemistry of d-block metals vacant d-orbitals in transition metals accept lone pairs from neutral or anionic ligands to form coordination complexes.

2Complete Combustion of Hydrocarbons

Hydrocarbon fuels such as propane (C₃H₈) undergo complete combustion in an excess supply of oxygen,
producing carbon dioxide and water while burning with a clean blue flame: C₃H₈ + 5 O₂ → 3 CO₂ + 4 H₂O.

3Incomplete Combustion and Carbon Monoxide Toxicity

In a limited supply of oxygen, hydrocarbons undergo incomplete combustion to yield soot (carbon) and toxic carbon monoxide (CO),
which binds irreversibly to haemoglobin and prevents oxygen transport in the blood.

4Fuel Cells vs. Direct Combustion

Electrochemical fuel cells combine fuels like hydrogen or small organic molecules directly with oxygen to produce electricity with high efficiency, avoiding thermal losses and noxious emissions associated with burning fossil resources.

5Transition Away from Fossil Resources

Fossil hydrocarbons are non-renewable energy resources, driving the development of renewable alternatives such as biofuels and metal-catalyzed catalytic fuel cells.

6Energy density

Energy released per unit mass or volume

7Chemical formula

Symbols and numbers showing the relative number of atoms of each element.

8Specific energy

The energy released per unit mass of fuel.

9Oxygen

A gas that relights a glowing splint.

10Metal

An element with a lattice of positive ions in a sea of delocalised electrons, usually shiny, conductive and malleable.

11Hydrocarbon

A compound containing hydrogen and carbon only.

12Compound

Two or more elements chemically combined in a fixed ratio.

13Non-renewable

Cannot be replaced in a human lifetime

14Complete combustion

Burning in plenty of oxygen to give carbon dioxide and water.

15Incomplete combustion

Burning in limited oxygen to give CO, soot and water.

16Carbon monoxide

A toxic gas that binds to haemoglobin.

Section 24 of 33Renewable and non-renewable resources

Renewable

Renewable replaced as quickly as or faster than used, such as wood, bioethanol, wind and solar energy.

Non-renewable

Non-renewable finite on a human time scale;
- coal, crude oil and natural gas formed from organisms over millions of years.

Sustainable

Sustainable meets present needs without compromising future generations.

Fossil fuels

Fossil fuels have a high energy density and are easy to transport and burn, but release CO₂, SO₂ and oxides of nitrogen.
- (from sulfur impurities)

Reasons for biofuels

Reasons for biofuels to cut pollution, reduce global warming and replace depleting fossil fuels.

Section 25 of 33Bioethanol

Production

Production yeast ferments plant sugars in the absence of oxygen: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂.

Separation

Separation ethanol is separated by fractional distillation.

Source of glucose

Source of glucose green plants make glucose by photosynthesis, 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.

Use

Use can be blended with petrol.

Fermentation

Fermentation is anaerobic.

Section 26 of 33Biodiesel and biogas

Biodiesel

Biodiesel a vegetable oil or animal fat (triglyceride) reacts with methanol by transesterification with a strong base catalyst to form fatty acid methyl esters and glycerol.
- (propane-1,2,3-triol)

Transesterification

Transesterification the reaction is reversible, so excess methanol is used and yields can reach 98%.

Biogas

Biogas organic waste broken down by microorganisms without oxygen gives mainly methane and CO₂.

Composition

Composition glucose gives biogas with 50% methane, C₆H₁₂O₆ → 3CO₂ + 3CH₄.

Advantages of biofuels	Disadvantages of biofuels
Renewable; made from crops that absorb CO₂	Land and water used instead of for food
Close to carbon neutral overall	Fertiliser and processing use energy and release greenhouse gases
Usable in existing engines as blends	Lower energy density than petrol or diesel

Carbon neutrality
- biofuels are not always carbon neutral because of farming, processing and transport.

Section 27 of 33Specific energy and energy density

Specific energy

Specific energy the energy released per unit mass (kJ g⁻¹), found by dividing |ΔH_c| by molar mass.

Energy density

Energy density the energy released per unit volume (kJ dm⁻³).

Ethanol versus octane

Ethanol versus octane ethanol is about 29.7 kJ g⁻¹ (1367 ÷ 46.07) and octane about 47.9 kJ g⁻¹ (5470 ÷ 114.2).

Oxygenated fuels

Oxygenated fuels alcohols release less energy per gram because they are already partly oxidised.

Hydrogen

Hydrogen has very high specific energy (about 120 kJ g⁻¹) but very low energy density as a gas, which makes storage difficult.

Section 28 of 33Fuel cells as an alternative

1Operation

Operation hydrogen is oxidised at one electrode and oxygen reduced at the other.

2Continuous running

Continuous running the cell works while fuel and oxygen are supplied, and energy is not stored in it.

3Electron flow

Electron flow electrons pass through the external circuit, and the only product is water.

4Efficiency

Efficiency chemical energy converts directly to electrical energy, which is more efficient than burning fuel to drive a heat engine.

5Limitation

Limitation the production, storage and distribution of hydrogen.

Section 29 of 33Comparing fuels

Fuel	Advantages	Disadvantages
Coal	Large reserves, cheap, easily stored	Most CO₂ per unit energy, SO₂, particulates, non-renewable
Crude oil products	High energy density, easily transported, many uses	Non-renewable, CO₂, CO and NO_x, spills
Natural gas	Burns cleanly, least CO₂ per unit energy of fossil fuels	Non-renewable, methane leaks, hard to store
Biofuels	Renewable, closer to carbon neutral	Farmland and water use, lower specific energy
Hydrogen	Only product is water, very high specific energy	Low energy density as gas, mostly made from fossil fuels

Section 30 of 33Deciding which fuel is best

Criteria

Criteria energy per gram, energy per unit volume for storage, CO₂ per kilojoule, availability and cost, and other products such as SO₂.

No single best

No single best hydrogen has the highest specific energy and forms only water but needs high-pressure storage, ethanol is renewable with lower energy density,
- and petrol is convenient but non-renewable.

Conclusion

Conclusion weigh the criteria against the use, such as aircraft, cars or home heating.

Section 31 of 33More from the specification

Section 32 of 33Key terms

Term	Meaning
Complete combustion	Combustion in excess oxygen giving CO₂ and H₂O.
Incomplete combustion	Combustion in limited oxygen giving CO and/or C as well as water.
Specific energy	The energy released per unit mass of fuel.
Energy density	The energy released per unit volume of fuel.
Biofuel	A fuel made from recently living biomass.
Greenhouse gas	A gas that absorbs infrared radiation emitted by the Earth.
Fuel cell	A cell converting the chemical energy of a continuously supplied fuel directly into electrical energy.

Term	Meaning
Complete combustion	Combustion in excess oxygen producing CO₂ and H₂O.
Incomplete combustion	Combustion in limited oxygen producing CO and/or C.
Oxidation	Reaction with oxygen.
Stoichiometry	The quantitative relationships from a balanced equation.
Molar mass	The mass of one mole of a substance.

Term	Meaning
Greenhouse gas	A gas that absorbs infrared radiation emitted by the Earth.
Enhanced greenhouse effect	Additional warming from human-made increases in greenhouse gases.
Infrared radiation	Long-wavelength radiation emitted by warm surfaces.
Thermal decomposition	The breakdown of a compound by heating.
Carbonic acid	H₂CO₃, formed when CO₂ dissolves in water.

Term	Meaning
Non-renewable	A resource used faster than it forms.
Bioethanol	Ethanol made by fermentation of plant sugars.
Transesterification	Reaction of an oil with an alcohol to give esters and glycerol.
Specific energy	Energy released per unit mass of fuel.
Energy density	Energy released per unit volume of fuel.
Fermentation	Anaerobic breakdown of sugar by yeast to ethanol and CO₂.

Section 33 of 33Exam technique

Forgetting the oxygen in an alcohol when balancing — count it on the reactant side.

Stating hydrogen forms in incomplete combustion — hydrogen is oxidised to water first.

Saying biofuels are always carbon neutral — farming and processing add CO₂.

Saying greenhouse gases trap the Sun's rays — they absorb infrared emitted by the Earth.

Forgetting the oxygen in the fuel when balancing alcohol combustion — count the oxygen in the alcohol too.

Using the mass ratio rather than the mole ratio — convert to moles first.

Using M(CO₂) = 28 — it is 44.01 g mol⁻¹.

Writing carbon dioxide for incomplete combustion — the products are CO and/or C.

Saying the greenhouse effect is caused by holes in the ozone layer — these are separate problems.

Writing that greenhouse gases trap the Sun's rays — they absorb infrared emitted by the Earth.

Using the mass of fuel rather than moles in the ratio — convert to moles first.

Ignoring the 4 : 1 mole ratio for butane — four moles of CO₂ form per mole.

Saying biofuels are always carbon neutral — farming, processing and transport release CO₂.

Confusing renewable with sustainable — sustainability also considers future generations.

Comparing energy per mole when per gram is needed — divide by molar mass.

Saying fermentation uses oxygen — it is anaerobic.

Last updated: 14 October 2026

Section 1 of 33Combustion reactions

Section 2 of 33Complete combustion

Section 3 of 33Incomplete combustion

Section 4 of 33Fossil fuels

Section 5 of 33Specific energy and enthalpy of combustion

Section 6 of 33Carbon dioxide and the greenhouse effect

Section 7 of 33Biofuels

Section 8 of 33Fuel cells

Section 9 of 33More from the specification

Section 10 of 33Combustion and reactivity with oxygen

Section 11 of 33Balancing combustion equations

Section 12 of 33Calculating the mass of carbon dioxide produced

Section 13 of 33Using the energy released

Section 14 of 33Combustion of alcohols

Section 15 of 33Carbon dioxide and the greenhouse effect link

Section 16 of 33More from the specification

Section 17 of 33Carbon dioxide formed by burning a fuel

Section 18 of 33Rising carbon dioxide and its sources

Section 19 of 33Greenhouse gases

Section 20 of 33Mechanism of the greenhouse effect

Section 21 of 33Effects and responses

Section 22 of 33Structuring answers on CO<sub>2</sub> and climate

Section 23 of 33More from the specification

Section 24 of 33Renewable and non-renewable resources

Section 25 of 33Bioethanol

Section 26 of 33Biodiesel and biogas

Section 27 of 33Specific energy and energy density

Section 28 of 33Fuel cells as an alternative

Section 29 of 33Comparing fuels

Section 30 of 33Deciding which fuel is best

Section 31 of 33More from the specification

Section 32 of 33Key terms

Section 33 of 33Exam technique

Marked practiceQuizzes for this lesson