Question 1: Define the term 'cracking' in the context of organic chemistry.

Answer: Cracking is the chemical process of breaking down large hydrocarbon molecules into smaller, more useful ones, such as alkenes and alkanes.

Question 2: Explain why cracking is an essential step in the refining of crude oil.

Answer: Cracking increases the yield of valuable petrol and other fuels from heavier hydrocarbons that are less useful or in excess in crude oil.

Question 1: Describe the main difference between thermal cracking and catalytic cracking.

Answer: Thermal cracking uses high temperatures and pressures to break down hydrocarbons, producing alkenes and alkanes, while catalytic cracking uses a catalyst to lower the temperature required and produce mainly branched alkanes and aromatics.

Question 2: Identify two advantages of catalytic cracking over thermal cracking.

Answer: Catalytic cracking operates at lower temperatures, saving energy, and produces higher-quality petrol with more branched alkanes and aromatics.

Question 1: Given the hydrocarbon C₁₆H₃₄ undergoes cracking to produce C₁₀H₂₂ and C₆H₁₂, calculate the total number of carbon and hydrogen atoms in the products.

Answer: C: 16; H: 34

Question 2: If 100 g of a heavy hydrocarbon undergoes cracking and produces 60 g of alkenes, what is the percentage yield of alkenes?

Answer: 60%

Question 1: List three safety precautions that should be observed during thermal cracking experiments.

Answer: Use of protective gloves and goggles, working in a well-ventilated area or fume hood, and ensuring equipment is properly maintained to prevent leaks or explosions.

Question 2: Describe one environmental concern associated with cracking processes and how it can be mitigated.

Answer: Emission of sulphur dioxide and other pollutants; mitigated by using desulphurisation techniques and catalytic converters.

Question 1: An oil refinery reports that after cracking, the yield of petrol increased by 25%, and the production of alkenes doubled. Explain how cracking contributes to this increase in petrol yield.

Answer: Cracking breaks down larger hydrocarbons into smaller, more volatile molecules like alkanes suitable for petrol. The process also produces alkenes, which are valuable intermediates for plastics and chemicals, thus increasing overall petrol yield and adding economic value.

Question 1: Describe how modern catalytic cracking units improve fuel production efficiency compared to older methods.

Answer: They operate at lower temperatures with catalysts, reducing energy consumption, increasing the yield of high-quality petrol, and producing fewer undesirable by-products.

Question 2: Suggest one recent technological advancement in cracking processes and its benefit.

Answer: The use of zeolite catalysts has improved selectivity and efficiency, leading to higher yields of desired hydrocarbons and lower environmental impact.