A Level Chemistry OCR Practice Exam

What is the process of cracking in chemistry?

1. The formation of saturated hydrocarbons

2. The combination of shorter-chained alkanes

3. The breaking down of long-chained hydrocarbons into shorter alkanes and alkenes

4. The polymerization of alkenes into larger molecules

The correct answer is: The breaking down of long-chained hydrocarbons into shorter alkanes and alkenes

Cracking in chemistry refers to the breaking down of long-chained hydrocarbons into shorter alkanes and alkenes. This process is crucial in the oil refining industry, where larger, less useful hydrocarbons obtained from crude oil are converted into more valuable products such as gasoline, diesel, and various chemicals. During cracking, heat, catalysts, or both are used to break the carbon-carbon bonds in the long hydrocarbons. This results in a mixture of shorter carbon chain molecules, which can include both saturated hydrocarbons (alkanes) and unsaturated hydrocarbons (alkenes). The other processes mentioned, such as the formation of saturated hydrocarbons, combination of shorter-chained alkanes, and polymerization of alkenes into larger molecules, do not accurately describe cracking. These options highlight different chemical reactions that do not involve the breakdown of long-chain hydrocarbons, which is the definitive characteristic of cracking.