Question 1: Define combustion in the context of hydrocarbons derived from crude oil.

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

Question 2: Explain why complete combustion of hydrocarbons 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 to carbon dioxide and water. Incomplete combustion occurs with limited oxygen, leading to partial oxidation and formation of carbon monoxide and soot (carbon particles).

Question 1: Calculate the energy released when 2 mol of methane (CH4) undergoes complete combustion. Given that the enthalpy change of combustion for methane is -890 kJ/mol.

Answer: 1780 kJ

Question 2: A litre of petrol (assumed density 0.75 g/cm³) contains approximately 800 g of hydrocarbons. If the combustion releases 44 MJ per kg of hydrocarbons, estimate the total energy released from burning 1 litre of petrol.

Answer: 35.2 MJ

Question 1: Identify three variables that can affect the completeness of combustion in a laboratory experiment involving hydrocarbons.

Answer: Amount of oxygen supplied, temperature of the flame, and the distance between the flame and the hydrocarbon source.

Question 2: List two safety precautions that must be followed when conducting combustion experiments involving hydrocarbons.

Answer: Ensuring proper ventilation and keeping a fire extinguisher nearby.

Question 1: A combustion experiment measuring the energy released shows a lower-than-expected value. Suggest two possible reasons for this discrepancy.

Answer: Incomplete combustion due to insufficient oxygen, or heat loss to surroundings during the experiment.

Question 1: Explain how understanding combustion reactions is important for controlling emissions from power stations.

Answer: Understanding combustion reactions allows engineers to optimise fuel burning to maximise energy output while minimising harmful emissions such as carbon monoxide, sulphur dioxide, and nitrogen oxides. Proper control of oxygen supply and fuel mixture helps reduce incomplete combustion and pollutant formation, contributing to environmental protection and compliance with regulations.