MHT CET · Chemistry · Hydrocarbons

The reactions of alkanes are explosive with which halogen?

A Fluorine
B Chlorine
C Bromine
D Iodine

Verified Solution

Answer & Solution

Correct Answer

(A) Fluorine

Step-by-step Solution

Detailed explanation

The reaction of alkanes with fluorine is difficult to control bacause the activation energy for hydrogen abstraction is so low.
The initiation step involves the homolytic cleavage of the

F - F

bond.

F - F \to \dot{F} + \dot{F}; E_{a} = + 155 k J / m o l

This is a high activation energy. But only a few

F

atoms need to form.
Each

F

atom can then initiate thousands of propagation steps.

C H_{4} + \dot{F} \to C H_{3} F + \dot{H}

These steps are highly exothermic;

Δ H^{o} = - 431 k J / m o l .

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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