A __________ is a thermally unstable reaction system which exhibits an uncontrolled accelerating rate of reaction leading to rapid increases in temperature and pressure.

• A. Exothermic reaction
• B. Runaway reaction
• C. Endothermic reaction
• D. Kinetic reaction

Answer: (B)

Runaway reaction describes a thermally unstable system where the reaction rate accelerates uncontrollably as heat is produced. Because the rate typically grows with temperature (Arrhenius behavior), if cooling is insufficient, temperature climbs, which speeds up the reaction further and releases more heat. This creates a positive feedback loop that drives rapid increases in both temperature and pressure, sometimes leading to an explosion. The other terms don’t capture this unstable, self-accelerating behavior: an exothermic reaction releases heat but isn’t inherently uncontrolled; an endothermic reaction consumes heat; and a kinetic reaction isn’t a standard descriptor for this specific runaway phenomenon.