A rigid, sealed flask at contains a shallow pool of liquid water in equilibrium with…
CHEMISTRY · Multi-part · A Level · Chemistry · Chemical equilibria (Le Chatelier’s principle and Kc) · Chemical equilibria (Le Chatelier’s principle and Kc)
Problem
A rigid, sealed 250mL flask at 25∘C contains a shallow pool of liquid water in equilibrium with its vapor. After the system has been allowed to stand undisturbed for several hours, the total pressure inside the flask is measured to be 23.8kPa, and neither the mass of liquid water nor the pressure changes with further time.
At the same temperature, a second sealed flask of identical volume contains an iron block resting motionless on the bottom surface. The normal force exerted by the bottom wall on the block exactly balances the block’s weight, and no macroscopic motion is observed.
Both systems appear "unchanging" from a macroscopic perspective.
(a) Cite the specific macroscopic evidence that indicates the water–vapor system has reached equilibrium.
(b) Describe, in terms of molecular-level behavior, what is occurring at the liquid–vapor interface *after* the equilibrium pressure of 23.8kPa has been established.
(c) Classify each system—the water–vapor system and the iron-block system—as exhibiting either *dynamic* equilibrium or *static* equilibrium. Justify each classification by referring explicitly to the microscopic or particulate-level processes (or lack thereof) occurring within the system.
(d) A student lightly shakes the first flask, temporarily disturbing the liquid surface but keeping the temperature constant. Predict and explain whether the measured pressure will (i) increase, (ii) decrease, or (iii) remain the same once the system returns to equilibrium.