A Level Chemistry OCR Practice Exam

Which term describes the two repeated steps during radical substitution?

1. Initiation

2. Termination

3. Propagation

4. Equilibrium

The correct answer is: Propagation

The term that describes the two repeated steps during radical substitution is propagation. In a radical substitution reaction, the propagation steps involve the continuous generation and reaction of radicals. During these steps, a radical reacts with a stable molecule, leading to the formation of a new radical and a different stable molecule. This cycle can repeat multiple times, allowing the substitution process to continue until the reaction reaches completion or is terminated by other means. The initiation step refers to the generation of radicals from non-radical species, typically through processes like homolytic bond cleavage. Termination involves the combination of radicals to form stable products, effectively ending the radical chain reaction. Equilibrium is a concept related to reversible reactions where the rates of the forward and reverse reactions are equal, which does not specifically describe the steps in radical substitution.