Question 1: Define combustion in the context of organic chemistry.

Answer: Combustion is a chemical reaction where a hydrocarbon reacts with oxygen to produce carbon dioxide, water, and energy.

Question 2: Explain why complete combustion produces only carbon dioxide and water, whereas incomplete combustion produces carbon monoxide and soot.

Answer: Complete combustion occurs when there is sufficient oxygen, allowing hydrocarbons to fully oxidise into carbon dioxide and water. Incomplete combustion happens with limited oxygen, leading to partial oxidation and the formation of carbon monoxide and soot (carbon particles).

Question 3: Describe the main environmental concerns associated with incomplete combustion of hydrocarbons.

Answer: Incomplete combustion releases carbon monoxide, which is poisonous, and soot, which contributes to air pollution and respiratory problems.

Question 1: Calculate the volume of carbon dioxide produced when 2 moles of methane (CH4) undergo complete combustion at room temperature and pressure. (Use the reaction: CH4 + 2O2 → CO2 + 2H2O).

Answer: At room temperature and pressure, 1 mole of gas occupies approximately 24 dm³. Therefore, 2 moles of CH4 produce 2 moles of CO2, which equals 2 × 24 dm³ = 48 dm³.

Question 2: If 25 grams of propane (C3H8) are completely combusted, calculate the mass of carbon dioxide produced. (Atomic masses: C = 12, H = 1).

Answer: Moles of C3H8 = 25 g / (3×12 + 8×1) = 25 / 44 ≈ 0.568 mol. Each mole produces 3 mol of CO2, so total CO2 = 0.568 × 3 ≈ 1.704 mol. Mass of CO2 = 1.704 mol × (12 + 16) g/mol ≈ 1.704 × 28 = 47.7 g.

Question 1: Describe a basic practical method to investigate the products of combustion of a hydrocarbon. Include variables to control and safety precautions.

Answer: Set up a sealed chamber with a hydrocarbon sample and oxygen, ignite the hydrocarbon, and collect gases for analysis. Control variables include oxygen supply, temperature, and hydrocarbon amount. Safety precautions involve wearing eye protection, working in a well-ventilated area, and handling flames carefully to prevent accidents.

Question 1: A sample of hydrocarbon burns with a yellow soot flame, producing a smoky exhaust containing carbon monoxide and soot. Explain what this indicates about the combustion process and potential environmental impact.

Answer: The yellow soot flame indicates incomplete combustion, which produces carbon monoxide and soot. This suggests limited oxygen supply, leading to pollution and health hazards due to toxic gases and particulate matter.

Question 1: Discuss how the combustion of hydrocarbons in engines contributes to air pollution, and suggest methods to reduce harmful emissions.

Answer: Hydrocarbon combustion in engines often results in incomplete combustion, releasing carbon monoxide, unburned hydrocarbons, nitrogen oxides, and soot, which contribute to smog, acid rain, and health issues. To reduce emissions, engines can be designed for complete combustion, use cleaner fuels, and employ catalytic converters to convert pollutants into less harmful substances.

Question 2: Explain why the combustion of fossil fuels is considered a major contributor to climate change and outline alternative energy sources that could mitigate this issue.

Answer: Fossil fuel combustion releases large amounts of carbon dioxide, a greenhouse gas that traps heat in the atmosphere, leading to global warming. Alternatives such as wind, solar, hydroelectric, and nuclear power produce little to no greenhouse gases and are more sustainable options to reduce climate change impacts.