Question 1: Combustion is a chemical process where a substance reacts rapidly with oxygen, releasing heat and light. Hydrocarbons, such as those found in crude oil, undergo combustion to produce carbon dioxide and water. This process is vital in energy production but also contributes to pollution.

Answer: Combustion is a rapid reaction with oxygen producing heat and light; hydrocarbons produce carbon dioxide and water.

Question 1: Define complete combustion of a hydrocarbon.

Answer: Complete combustion occurs when a hydrocarbon reacts fully with oxygen, producing carbon dioxide and water.

Question 2: Explain why incomplete combustion produces carbon monoxide instead of carbon dioxide.

Answer: Incomplete combustion occurs when there is insufficient oxygen, leading to the formation of carbon monoxide instead of carbon dioxide.

Question 1: Calculate the amount of carbon dioxide produced when 10 g of methane (CH₄) undergoes complete combustion. (Molar mass of CH₄ = 16 g/mol, CO₂ = 44 g/mol)

Answer: 11.0 g of CO₂

Question 2: If 100 g of octane (C₈H₁₈) is burned completely, how many grams of water are produced? (Molar mass of C₈H₁₈ = 114 g/mol, H₂O = 18 g/mol)

Answer: 142.0 g of H₂O

Question 1: Describe the key safety precautions that should be taken when conducting a combustion experiment in the lab.

Answer: Use safety goggles, conduct experiments in a well-ventilated area, keep flammable materials away from open flames, and have a fire extinguisher nearby.

Question 2: Identify the variables that could affect the completeness of hydrocarbon combustion in a controlled experiment.

Answer: Oxygen supply, temperature, hydrocarbon purity, and airflow conditions.

Question 1: A combustion experiment reports a 20% excess of oxygen in the reaction mixture. Explain how this excess oxygen affects the products of combustion.

Answer: Excess oxygen promotes complete combustion, ensuring that hydrocarbons are fully oxidised to carbon dioxide and water, reducing carbon monoxide formation.

Question 1: Write the balanced chemical equation for the complete combustion of ethane (C₂H₆).

Answer: 2 C₂H₆ + 7 O₂ → 4 CO₂ + 6 H₂O

Question 2: A litre of methane (at room temperature and pressure) reacts with excess oxygen. Calculate the volume of carbon dioxide produced, assuming ideal gas behaviour (molar volume = 24 dm³).

Answer: 48 dm³ of CO₂

Question 3: Explain the environmental impact of incomplete combustion of hydrocarbons in terms of pollutant formation.

Answer: Incomplete combustion produces carbon monoxide, which is toxic, and particulate soot, contributing to air pollution and health hazards. It also releases unburnt hydrocarbons, which can form smog.

Question 1: Describe how understanding combustion reactions is important for designing cleaner-burning fuels and reducing pollution.

Answer: By understanding combustion, scientists can develop fuels that burn more completely, reducing harmful emissions like carbon monoxide and soot, and designing engines that are more efficient.