Unit 3 Chemistry A0S 1: Carbon-Based Fuels Study Notes

Unit 3 Chemistry A0S 1: Carbon-Based Fuels

Contents

• Fossil Fuels

• Biofuels

• Fuel for the body

• Enthalpy changes and combustion reactions

Key Knowledge

• Fuel Definition:

  • A fuel is a substance that releases energy, usually in the form of heat, when it is combusted.

  • Distinguishing between fossil fuels and biofuels:

  • Fossil Fuels: Non-renewable resources formed from the decomposition of organic matter over millions of years, including coal, natural gas, and petrol.

  • Biofuels: Renewable resources that can be replaced more easily. Examples include biogas, bioethanol, and biodiesel.

  • Renewability: The ability of a resource to be replaced by natural processes within a relatively short period of time.

• Fuels for the Body:

  • Energy content measured in kJ/g for the following components:

  • Carbohydrates

  • Proteins

  • Lipids (fats and oils)

• Photosynthesis:

  • Chemical process outlined by the equation:
    $6CO₂(g) + 6H₂O(l) → C₆H₁₂O₆(aq) + 6O₂(g)$

  • Converts light energy into chemical energy, creating glucose and oxygen for respiration.

• Oxidation of Glucose:

  • Primary carbohydrate energy source measured with the equation for cellular respiration:
    $C₆H₁₂O₆(aq) + 6O₂(g) → 6CO₂(g) + 6H₂O(l)$

• Bioethanol Production:

  • Generated by the fermentation of glucose followed by distillation to create a sustainable fuel:
    $C₆H₁₂O₆(aq) → 2C₂H₅OH(aq) + 2CO₂(g)$

• Exothermic vs. Endothermic Reactions:

  • Understanding enthalpy changes (ΔH) in kJ:

  • Exothermic: ΔH < 0 (releases energy)

  • Endothermic: ΔH > 0 (absorbs energy)

  • Representation through energy profile diagrams involving bond-making and bond-breaking processes.

• Limiting Reactants:

  • Identification in chemical reactions that determines the amount of product formed.

• Combustion Reactions of Fuels:

  • Combustion can be complete or incomplete, both categorized as exothermic.

  • Balanced thermochemical equations must include states for completing combustion of organic molecules based on experimental data.

Chapter 1 Ticksheet

Learning Activities

1. Fossil Fuels and Coal

   • Goal: Understanding fossil fuels and their renewability.

2. Oil and Natural Gas

   • Goal: Comprehending definitions and renewability in fossil fuels.

3. Biofuels

   • Goal: Distinguishing biofuels from fossil fuels concerning renewability.

4. Fuel for the Body

   • Goal: Understanding substrates used by the body for energy.

5. Enthalpy Changes and Combustion Reactions

   • Goal: Distinguishing enthalpy definitions in complete vs incomplete combustion.

6. Enthalpy Changes

   • Goal: Comparing exothermic and endothermic reactions with enthalpy changes.

Glossary

• Chemical Decomposition: Breaking larger chemical species into simpler molecules.

• Coal: Combustible fossil fuel formed by partial decay of plant/animal matter.

• Coal Seam Gas: Natural gas sourced from coal deposits.

• Crude Oil: Black mixture of hydrocarbons.

• Enhanced Greenhouse Effect: Warming caused by increased gas concentrations in the atmosphere.

• Fossil Fuel: Natural fuel formed under Earth's crust from decomposed remains.

• Natural Gas: A fossil fuel comprising small hydrocarbon molecules, primarily methane ($CH₄$).

• Non-Renewable Resource: Resources not replaced by natural processes quickly.

• Petrol: Purified liquid hydrocarbon fossil fuel from crude oil.

• Petroleum: Complex hydrocarbon mixture found in the Earth.

• Sustainable: Produced without compromising future resources.

Energy Overview

• Definition of Energy: The capacity to perform work.

  • Measured in:

  • Joules (J)

  • Kilojoules (kJ)

  • Megajoules (MJ)

  • Gigajoules (GJ)

  • Terajoules (TJ)

Meeting Energy Needs

• Fuels are crucial sources of readily available chemical energy.

• Fossil fuels, notably coal, oil, and natural gas, account for nearly 90% of world energy production, but this leads to increased greenhouse gas emissions and dependency on finite resources.

  • The main pressures to reduce reliance on fossil fuels stem from:

  • Greenhouse gas and sulfur dioxide production, contributing to acid rain.

  • Their non-renewable nature.

  • Demand for petroleum in the manufacture of polymers and other products.

Renewable vs Non-Renewable Sources

• Renewable Sources:

  • Solar

  • Wind

  • Tidal

  • Hydro

  • Geothermal

  • Biogas

  • Batteries and fuel cells

• Non-Renewable Sources:

  • Coal

  • Petroleum

  • Natural Gas

  • Nuclear fission and fusion

Law of Conservation of Energy

• Energy cannot be created or destroyed; it can only change forms.

  • Various forms include electrical, gravitational, elastic, nuclear, light, heat, chemical, sound, and kinetic energy.

• Example: In a car engine, chemical energy converts to thermal energy, with only about 20-25% of the energy converting to mechanical energy.

Fossil Fuel Formation

Coal

• Formed from the decomposition of plant matter over millions of years under varying conditions.

• Stages:

  • Peat formation from decomposed plant layers

  • Pressure and anaerobic conditions eventually leading to coal.

Composition of Coal

• Peat: 10-15% Carbon, 75-80% Water

• Brown Coal: 20-30% Carbon, 50-70% Water

• Black Coal: 70-80% Carbon, 5-10% Water

• Anthracite: 85-90% Carbon, 2-5% Water

• Energy Content: Increases with higher carbon content.

Uses of Coal

• Major energy source in Australia, with approximately 80% of electricity generated from coal.

  • Functioning through sequential energy transformations:

  • Chemical energy in coal → Thermal energy from combustion → Mechanical energy in turbines → Electrical energy output.

Pollution Problems with Coal

• Coal combustion produces pollutants such as sulfur dioxide, nitrogen oxides, and particulates.

• Sulfur and nitrogen oxides can lead to acid rain:

  • Example reactions involve hydrolysis of oxides with water, generating acids.

Coal Reserves

• Distribution of reserves globally includes:

  • Coal: $1 imes 10^{12}$ tonnes, lifetimes ranging up to 250 years.

  • Oil: $1 imes 10^{11}$ tonnes, lifetimes of 40-100 years.

  • Natural gas: $1 imes 10^{11}$ tonnes, lifetimes of 45-75 years.

Crude Oil and Natural Gas

Crude Oil (Petroleum)

-Mixture: Composed of various hydrocarbons; separated through fractional distillation.

• Fractional Distillation:

  • Process where oil heated to separate lighter fractions through vaporization-condensation principles.

Natural Gas

• Primarily contains methane ($CH₄$), used extensively for heating.

  • Lower CO₂ emissions compared to coal-fired plants and fewer pollutants.

Biofuels

Definition and Formation

• Derived from organic materials (biomass), including plant waste and animal fats.

• Considered renewable as they are sourced sustainably and largely help mitigate carbon emissions.

  • Main types: ethanol and biodiesel.

Production of Biofuels

• Ethanol: Produced through fermentation of glucose.

  • Equation:
    $C₆H₁₂O₆(aq) → 2C₂H₅OH(aq) + 2CO₂(g)$

  • Processes such as distillation refine the product for fuel use.

• Biodiesel: Generated via transesterification of triglycerides.

  • Mixture of esters reacted with alcohol (often methanol) in the presence of a strong base.

Carbon Neutral Concept

• Biofuels are carbon neutral as combustion releases CO₂ that plants absorbed during growth.

Check In Questions

1. What is a fuel?

2. Describe the process of fractional distillation.

3. How is bioethanol produced?

4. Explain why biofuels are considered renewable.

5. Discuss the benefits of using biodiesel.

Energy Changes during Chemical Reactions

• Enthalpy (H): Heat content of a substance.

• Reaction types determine energy flow:

  • Exothermic: ΔH < 0 (energy released)

  • Endothermic: ΔH > 0 (energy absorbed)

Combustion Reactions

• All combustion processes lead to oxidation reactions resulting in heat and energy production.

• Balanced Equation for Complete Combustion:

  • For hydrocarbons:
    $C<em>nH</em>m + O_2 → CO₂ + H₂O$