Question

For the radical chain reaction below, the correct classification for step 2 and step 3 is, respectively,
Step 1: \( \text{Br}_2 + M \longrightarrow 2 \text{Br}^+ + M \)
Step 2: \( \text{Br}^+ + \text{H}_2 \longleftrightarrow \text{HBr} + \text{H}^+ \)
Step 3: \( \text{H}^+ + \text{Br}_2 \longrightarrow \text{HBr} + \text{Br}^+ \)

• A. chain propagating, chain terminating
• B. chain branching, chain terminating
• C. chain propagating, chain propagating
• D. chain propagating, chain branching

Hint:

In radical chain reactions, "chain propagating" refers to steps that produce more radicals, "chain branching" refers to steps that increase the number of radicals, and "chain terminating" refers to steps that consume radicals.

Answer 1

The Correct Option is C

Step 1: Understanding the radical chain reaction.
In a radical chain reaction, certain steps are classified as "chain propagating," "chain branching," or "chain terminating" based on how they affect the chain of reactions.

Step 2: Analyzing step 2 and step 3.

Step 2: The reaction \( \text{Br}^+ + \text{H}_2 \longleftrightarrow \text{HBr} + \text{H}^+ \) involves the consumption of radicals and the formation of new radicals, indicating a propagation of the chain reaction. Hence, step 2 is "chain propagating."

Step 3: The reaction \( \text{H}^+ + \text{Br}_2 \longrightarrow \text{HBr} + \text{Br}^+ \) also propagates the chain by generating more radicals. Thus, step 3 is "chain propagating."

Step 3: Conclusion.
Both steps 2 and 3 are chain propagating reactions, so the correct classification is (C).