The chemical reaction initiated by a threshold cannot be stopped until completion when the material reaches which point?

• A. Equilibrium
• B. Critical point
• C. Boiling point
• D. Melting point

Answer: (B)

When a chemical reaction is started by a threshold, it can become self-sustaining if heat released by the reaction pushes the system toward conditions where the reaction feeds on itself. The point at which this self-accelerating behavior becomes unavoidable—where the rate of heat generation outpaces the system’s ability to remove heat, and the reaction proceeds to completion regardless of attempts to stop it—is the critical point. At this point, temperature and pressure reach levels that drive the reaction forward, making stopping the process impractical or impossible.

Equilibrium describes a balance between forward and reverse reactions, not a runaway scenario. Boiling and melting points are about phase changes, not whether a reactive process will continue once started.