Question

What is the equilibrium vapor pressure of a liquid? How is it measured?

Answer 1

basically it's the pressure at which there is equilibrium between the gaseous and liquid phases. Higher vapor pressures generally indicate the liquid is volatile and has weaker forces holding the molecules together.

Answer 2

For the measurement: http://www.csun.edu/~ml727939/coursework/695/vapor%20pressure/Vapor%20Pressure.htm