A Level Chemistry OCR Practice Exam

What is the term for the initial step in a radical substitution process?

1. Propagation

2. Termination

3. Initiation

4. Reformation

The correct answer is: Initiation

The term for the initial step in a radical substitution process is initiation. During this phase, radicals are generated, typically through the homolytic cleavage of covalent bonds, often induced by heat, light, or chemical initiators. This step is crucial because it provides the free radicals that will drive the subsequent steps of the reaction. Knowing that initiation leads to the formation of reactive intermediates helps to understand how radical substitution reactions proceed. The radicals generated then participate in the propagation steps where they react with stable molecules to produce new radicals, continuing the cycle. The termination step occurs later when two radicals combine to form a stable product, effectively stopping the reaction. Reformation isn’t a standard term used in radical substitution processes. Therefore, understanding initiation is key to grasping the overall mechanism of radical reactions.