International General Certificate of Secondary Education (IGCSE) Chemistry Practice Exam

Which of the following is a condition for the cracking of hydrocarbons?

1. Temperature of 200°C

2. Use of a zinc catalyst

3. Aluminium oxide catalyst heated to 600°C

4. Pressure of 10 atm

The correct answer is: Aluminium oxide catalyst heated to 600°C

The cracking of hydrocarbons is a process used to break down larger alkane molecules into smaller, more useful hydrocarbons, such as alkenes and shorter alkanes. A key requirement for this process is the presence of a suitable catalyst and the right temperature. Using aluminum oxide as a catalyst is appropriate for the cracking process, as it facilitates the breaking of the carbon-carbon bonds. The temperature of around 600°C is crucial because it provides enough energy to overcome the activation energy required for the breaking of these bonds. Cracking at this temperature leads to efficient conversion and optimization of the products, making it a common practice in industrial applications. In contrast, the other conditions provided are not suitable for the efficient cracking of hydrocarbons. For instance, a temperature of 200°C is generally too low for effective cracking, as the energy at this temperature may not be sufficient to promote the necessary reactions. The use of a zinc catalyst is not standard for this process and does not provide the same effectiveness as aluminum oxide. Lastly, a high pressure of 10 atm is typically not required and could complicate the process without enhancing the yield significantly. Overall, the condition of using aluminum oxide as a catalyst heated to 600°C is essential for the efficient cracking of