This question is about the reactions of alkanes - AQA - A-Level Chemistry - Question 1 - 2018 - Paper 2

A suitable catalyst for the catalytic cracking of hexadecane is zeolite or aluminosilicate.

One condition for this process is using slight or moderate pressure.

The equation for the catalytic cracking of hexadecane is:

$C_{16}H_{34} \rightarrow C_7H_{16} + C_6H_{12} + C_3H_8$

(where $C_6H_{12}$ is cyclohexane and $C_3H_8$ is propane).

The propagation steps for the chlorination of butane to form 2-chlorobutane are:

1. Formation of a radical: $C_4H_{10} + Cl^{\bullet} \rightarrow C_3H_{7}^{\bullet} + HCl$

2. Reaction of the radical with chlorine: $C_3H_{7}^{\bullet} + Cl_2 \rightarrow C_3H_7Cl + Cl^{\bullet}$

The radical produced from CFCs responsible for ozone depletion is the chlorine radical, Cl.

A single chlorine radical can cause the decomposition of many ozone molecules by acting as a chain reaction catalyst. The mechanism involves:

1. The reaction of the radical with ozone: $Cl^{\bullet} + O_3 \rightarrow ClO^{\bullet} + O_2$

2. The reaction of the chlorine monoxide radical with another ozone molecule: $ClO^{\bullet} + O_3 \rightarrow Cl^{\bullet} + 2O_2$

In this way, one chlorine radical can destroy numerous ozone molecules.