Vapor Pressure Over Concave Surface Explained

The vapor pressure of a liquid depends on the curvature of its surface. Surface tension causes differences in vapor pressure between curved and flat surfaces.

Surface Forces and Curvature

Consider the intermolecular forces acting on molecules at the liquid surface:

• Plane Surface: Molecules are pulled equally by neighbors, resulting in a baseline vapor pressure.
• Concave Surface: Molecules at the surface experience an increased inward pull from the surrounding liquid due to the surface curvature. This enhanced attraction makes it harder for molecules to escape into the vapor phase.

Vapor Pressure Comparison

Because the inward pull is stronger on a concave surface, fewer molecules can escape into the vapor. This leads to:

The vapor pressure over a concave surface is less than the vapor pressure over the plane surface.

Conversely, a convex surface (like a droplet) has a vapor pressure greater than that over a plane surface.