Flash vaporization occurs when a liquid near its boiling point experiences what change?

• A. A drop in pressure causing rapid vaporization
• B. A decrease in temperature
• C. An increase in liquid viscosity
• D. An increase in ambient humidity

Answer: (A)

Flash vaporization happens when a liquid that is already near its boiling point is suddenly subjected to a drop in ambient pressure. At that temperature the liquid’s vapor pressure is high, so lowering the surrounding pressure below that level means the liquid can no longer stay in liquid form. Vapor forms rapidly, so the liquid “flashes” into vapor almost instantly. The key idea is that the reduced pressure removes the restraint on vapor formation when the liquid is ready to boil. Cooling, increasing viscosity, or higher humidity don’t trigger this rapid transition in the same way, because they don’t push the system across the threshold where vapor pressure exceeds ambient pressure.