When large hydrocarbon molecules are heated at high temperature in the presence of a catalyst to give smaller molecules, the process is known as

Analysis

The question asks for the specific term used to describe the industrial process of breaking down large, heavy hydrocarbon molecules into smaller, more useful molecules (like petrol or ethene) using high heat and a catalyst.

Concept Explanation

In petroleum chemistry, the demand for shorter-chain hydrocarbons (which are used as fuel for cars) is much higher than the supply obtained from fractional distillation of crude oil. To bridge this gap, refineries use a process called cracking.

• Cracking involves heating long-chain alkanes (which have high boiling points and are less valuable) to high temperatures, often in the presence of a catalyst (like silica or alumina).
• This process breaks the carbon-carbon bonds, resulting in smaller, more volatile, and more valuable molecules like alkanes and alkenes.

Let's look at why the other options are incorrect:

• Disintegration: This is a general term for breaking apart, not a specific chemical process in petroleum refining.
• Polymerization: This is the exact opposite of cracking. It involves joining many small monomer molecules together to form a large polymer chain.
• Degradation: This usually refers to the breakdown of materials due to environmental factors (like weathering or biological decay), not a controlled industrial chemical process.

Step-by-Step Solution

1. Identify the input: Large hydrocarbon molecules (long-chain alkanes).
2. Identify the conditions: High temperature and a catalyst.
3. Identify the output: Smaller molecules.
4. Match with the process: The chemical process defined by breaking large molecules into smaller ones under these specific conditions is cracking.

Conclusion

The process described is the standard definition of cracking in organic chemistry.

Exam Tip: Always remember the "Cracking vs. Polymerization" pair. Cracking = Breaking (Large to Small). Polymerization = Building (Small to Large). This simple association will help you answer similar questions in your JAMB exam easily.