Chemistry Chapter on Combustion of Methane

Chapter 6: Energy from Combustion

• Combustion reactions typically involve hydrocarbons reacting with oxygen to produce carbon dioxide and water.
• Example: Methane Combustion CH4 + 2O2 → CO2 + 2H2O
• To balance combustion reactions, follow these steps:
  • Write the equation (e.g., Methane + Oxygen → Carbon Dioxide + Water).
  • Count the atoms on each side of the equation before and after the reaction (e.g., C, H, O).
  • Balance the atoms by adjusting the coefficients for each molecule until the number of each atom is equal on both sides of the equation.
• Kinetic Energy: Energy of motion.
• Potential Energy: Stored energy due to position or composition.
• Heat: Energy flowing from a hotter object to a cooler one.
• Temperature: Measurement of average kinetic energy of molecules.
• Calorie: Energy to raise 1 g of water by 1 °C.
• Calorie (Cal): 1 nutritional Calorie = 1 kcal = 1000 cal.
• Joule (J): SI unit of energy. 1 cal = 4.184 J.
• Kilojoule (kJ): 1 kJ = 1000 J.
• Calorimeter: Instrument to measure the heat of combustion.
• Exothermic Reaction: Releases heat during a reaction (e.g., combustion).
• Endothermic Reaction: Absorbs heat during a reaction (e.g., photosynthesis).
• Finding kJ/g:
  • Write down known information (molecular formula and energy released).
  • Calculate the mass of one mole of the substance.
  • Use the given values to calculate kJ/g.

How to Draw Lewis Structures

• Lewis structures show how atoms bond and share electrons.
• Steps:
  • Count valence electrons for each atom.
  • Connect atoms with single bonds (each bond = 2 electrons).
  • Complete octets for each atom (except hydrogen, which needs 2).
  • Adjust if needed to ensure the correct number of electrons.

Exothermic vs. Endothermic Combustion Reactions

• Combustion reactions involve a fuel (hydrocarbon) reacting with oxygen to produce carbon dioxide and water.
• Exothermic combustion: Releases heat (products have lower energy than reactants). Most combustion reactions are exothermic.
• Endothermic combustion: Absorbs heat (products have higher energy than reactants).

Calculate Heat of Combustion

• Calculate using bond energies (Table 5.1).
• List bonds broken (reactants) and bonds formed (products).
• Calculate total energy (Heat of Combustion = Bonds Broken - Bonds Formed).

Summary of Lewis Structures & Combustion

• Lewis structures illustrate the bonding and electron sharing within molecules.
• Combustion reactions (e.g., burning methane) involve hydrocarbon fuels reacting with oxygen to create certain products and release a significant amount of energy.

Chapter 7: Energy from Alternative Sources

• Nuclear Fission: Splitting heavy nuclei to release energy. Chain Reaction: Continuous fission process.
  • Balancing Nuclear Equations: Balance mass numbers (top numbers) and atomic numbers (bottom numbers) on both sides of the equation.
  • Alpha Decay: Mass number decreases by 4, atomic number decreases by 2.
  • Beta Decay: Mass number remains the same, atomic number increases by 1. Radioactive Isotopes decay to reach stability.
  • Half-Life: Time for 50% decay of a radioactive isotope.
  • Radioactive Decay Series: A sequence of decays until a stable nucleus is reached.
• Nuclear Power Plants: Utilize nuclear fission to generate electricity.
• Nuclear waste storage is a complex issue.
• Common decay series (e.g., Uranium-238, Thorium-232, Uranium-235) are often used in dating methods and require careful handling.

Photovoltaic (PV) Cells

• Photovoltaic (PV) cells convert light energy (sunlight) into electrical energy. This process involves light knocking electrons loose from atoms, creating an electric current.
• Semiconductor materials (often silicon) absorb photons in the PV cell.
• The absorbed photons excite electrons, causing them to move.
• This movement results in an electric current, which then power electrical devices.
• Doping creates specific layers in the PV cells to enhance electricity generation.

Renewable Energy Sources

• Renewable energy sources include wind, hydropower, geothermal, and biomass.
• These sources rely on sustainable energy resources without depleting natural resources.

Nuclear Incidents

• Nuclear accidents have occurred. Accidents, such as Chernobyl or Three Mile Island resulted in undesirable environmental impacts.

Yucca Mountain Nuclear Waste Repository

• A potential long-term nuclear waste repository in Nevada.
• Concerns include safety, seismic activity, and transport risks.