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AECHE Task 3 Cheatsheet

21/02/2026

AECHE Task 3 Cheatsheet

Task 3 – Extended Response (Biofuels) Student Name: Abdullah Arafat Teacher: Br. Kareem Part 1: Definitions & Fundamentals Definitions Renewable fuels are energy sources that can be replenished by natural processes at a rate equal to or faster than they are consumed. Conversely, non-renewable fuels are consumed faster than they can be naturally replenished, meaning they will eventually be depleted. Biofuels are fuels made from living organisms or a by-product of the waste they produce. Today’s biofuels primarily come from processing food crops such as corn, sugarcane, rapeseed, and soya. Additionally, biofuels currently being produced from waste vegetable oil are also sustainable. Fuel Examples in Australia

  • Renewable (Biofuels): Bioethanol, Biodiesel, Biogas.
  • Non-Renewable (Fossil Fuels): Petrodiesel, Natural Gas, standard fossil-derived Ethanol. Advantages of Using Biofuels
  • They are derived from renewable resources, ensuring long-term sustainability compared to finite fossil fuels.
  • They are generally carbon neutral, helping to mitigate the overall increase in atmospheric greenhouse gases.
  • They can be produced domestically, reducing reliance on imported crude oil and enhancing national energy security. Disadvantages of Using Biofuels
  • Large-scale production often requires significant arable land, which can compete with global food production and drive up food prices.
  • The harvesting, transportation, and chemical processing of biofuel crops currently still rely heavily on energy derived from fossil fuels. Part 2: Production of Biofuels Bioethanol Bioethanol is produced via the fermentation of sugars (such as glucose) derived from crops.
  • Conditions: This requires an aqueous environment, anaerobic conditions (absence of oxygen), warm temperatures (around 30-40°C), and the presence of yeast as a biological catalyst.
  • Chemical Reaction: Biodiesel Biodiesel is produced through a process called transesterification. Triglycerides (fats or oils) are reacted with an alcohol (typically methanol).
  • Conditions: This reaction requires a strong base catalyst (such as potassium hydroxide or sodium hydroxide) and gentle heat.
  • Chemical Reaction: Biogas Biogas is generated through the anaerobic digestion of organic waste materials.
  • Conditions: It requires a strict anaerobic environment, controlled warm temperatures, and specific methanogenic bacteria to break down the organic matter.
  • Chemical Reaction (Simplified): Complex organic matter breaks down into primarily methane gas and carbon dioxide:

Part 3: Physical Properties & Intermolecular Forces The physical properties of biofuels and their fossil fuel counterparts are directly linked to their intermolecular forces. Differences in polarity between different types of fuels dictate the specific forces involved. If a fuel is polar, it exhibits stronger dipole-dipole forces or hydrogen bonding. If a fuel is non-polar, it relies solely on weaker dispersion forces.

  • Viscosity: This property describes which liquid is higher or lower in thickness. Viscosity is higher in the fuel that is slightly more polar. For example, biodiesel has a higher viscosity than petrodiesel because the ester groups in biodiesel are slightly polar (allowing dipole-dipole interactions), whereas petrodiesel is non-polar.
  • Solubility in Water: Solubility relates to whether fluids are miscible or immiscible, which is dependent on their polar and non-polar nature. Solubility is higher in the fuel that is slightly more polar. Bioethanol is highly soluble in water due to strong hydrogen bonding, whereas petrodiesel is immiscible.
  • Boiling Point / Melting Point: A higher boiling or melting point is due to having dipole-dipole forces compared to weaker dispersion forces. However, higher mass can also have an effect on this if the fuels have the same forces (for example, if both fuels were non-polar, the heavier one would have a higher boiling point).
  • Vapor Pressure: Vapor pressure indicates how likely it is for the fuel to become a gas. The relationship is inverse: the higher the boiling/melting point, the lower the vapour pressure. Because polar biofuels like bioethanol have stronger intermolecular forces and higher boiling points relative to their mass, they exhibit lower vapor pressures than non-polar equivalents. Part 4: Environmental Impacts & Greenhouse Emissions The Greenhouse Effect The burning of fuels enhances the greenhouse gas effect in detail via the production of carbon dioxide and water vapour. These gases trap thermal energy in the Earth’s atmosphere. Carbon Neutrality Biofuels are considered carbon neutral. This means that even if they produce greenhouse gas emissions (and even if it may be more than normal fuels), the greenhouse gas emissions produced are cancelled out. This happens because the carbon dioxide released during combustion was originally absorbed from the atmosphere by the plants (via photosynthesis) while they were growing, resulting in no net addition of new carbon to the atmosphere. Part 5: Fuel Comparisons
  1. Bioethanol vs. Ethanol

  • Combustion Reaction: Both fuels share the same chemical structure.

  • Heat of Combustion per Mole: Assuming \Delta H \approx -1367 \text{ kJ/mol}.

    • Heat released per mole of CO_2: 1367 / 2 = 683.5 \text{ kJ}
    • Heat released per mole of H_2O: 1367 / 3 = 455.7 \text{ kJ}

  • Greenhouse Emissions: Produces 2 moles of CO_2 and 3 moles of water vapour per mole of fuel combusted.

  • Which is better and Justification: Bioethanol is better for the environment. While the chemical outputs and energy released are identical, bioethanol is carbon neutral, whereas fossil-derived ethanol introduces ancient carbon into the modern atmosphere.

  1. Biogas vs. Natural Gas

  • Combustion Reaction: Both are primarily composed of methane (CH_4).

  • Heat of Combustion per Mole: Assuming \Delta H \approx -890 \text{ kJ/mol}.

    • Heat released per mole of CO_2: 890 / 1 = 890 \text{ kJ}
    • Heat released per mole of H_2O: 890 / 2 = 445 \text{ kJ}

  • Greenhouse Emissions: Produces 1 mole of CO_2 and 2 moles of water vapour per mole of fuel combusted.

  • Which is better and Justification: Biogas is better for the environment. It captures methane (a highly potent greenhouse gas) from decomposing waste that would otherwise enter the atmosphere, and it is entirely carbon neutral compared to extracting new fossil natural gas.

  1. Biodiesel vs. Petrodiesel
  • Comparisons: Biodiesel contains ester groups with oxygen, meaning it is partially oxidized before combustion. This results in a slightly lower overall heat of combustion per mole compared to the purely hydrocarbon petrodiesel.
  • Which is better and Justification: Biodiesel is better for the environment. It is renewable, carbon neutral, and typically produces fewer particulate and sulfur emissions upon combustion compared to petrodiesel. Part 6: Thermochemical Reaction & Energy Profile Balanced Thermochemical Reaction Using the combustion of methane (Biogas/Natural Gas) as the example fuel:

Energy Profile Diagram Because combustion is an exothermic reaction, the enthalpy diagram must show a negative change in enthalpy, with the products resting at a lower energy state than the reactants. Would you like me to draft a quick set of flashcards based on this document so you can test yourself on the intermolecular forces before Tuesday?