The other parameters are:γ the surface tension, the molar volume of the liquid, R the gas constant, and T the absolute temperature.

### The Kelvin Effect

Atoms of liquid on the surface of a small droplet are held less tightly compared to atoms on a flat (bulk) liquid surface. High curvatures effectively reduce the coordination number of the surface atoms making them easier to evaporate. Thus the liquid has a higher vapor pressure over small liquid droplets compared to bulk liquid. The effect of curvature on the vapor pressure of liquids is the Kelvin effect.

Positive curvature: liquid in drops has a higher vapor pressure that bulk.

Negative curvature: liquid in pores has a lower vapor pressure than bulk.

The vapor pressure P relative to the bulk P0 can be found using the Kelvin equation, show here for spherical surfaces of radius r.