What is vapor pressure, what causes it?

Question

Explain it as detailed as possible.

Answer 1

the molecules in the liquid phase have energy. This energy pushes up to the surface of the liquid as the molecules try to escape. The surrounding pressure pushes back.

The upward push from the liquid is called vapor pressure. As the temp. increases, this vapor pressure increases until it equals the surrounding pressure. Then the molecules begin to escape and the liquid "boils".

Answer 2

Vapor pressure is the pressure of a vapor in equilibrium with its non-vapor phases. All solids and liquids have a tendency to evaporate to a gaseous form, and all gases have a tendency to condense back. At any given temperature, for a particular substance, there is a partial pressure at which the gas of that substance is in dynamic equilibrium with its liquid or solid forms. This is the vapor pressure of that substance at that temperature.

In meteorology, the term vapor pressure is used to mean the partial pressure of water vapor in the atmosphere, even if it is not equilibrium,[1] and the equilibrium vapor pressure is specified as such. Meteorologists also use the term saturation vapor pressure to refer to the equilibrium vapor pressure of water or brine above a flat surface, to distinguish it from equilibrium vapor pressure which takes into account the shape and size of water droplets and particulates in the atmosphere.[2] This article is about our first definition of vapor pressure, or what meteorologists would call equilibrium vapor pressure.

Equilibrium vapor pressure is an indication of a liquid's evaporation rate. It relates to the tendency of molecules and atoms to escape from a liquid or a solid. A substance with a high vapor pressure at normal temperatures is often referred to as volatile. The higher the vapor pressure of a material at a given temperature, the lower the boiling point.

The vapor pressure of any substance increases non-linearly with temperature according to the Clausius-Clapeyron relation. The boiling point of a liquid is the temperature where the vapor pressure equals the ambient atmospheric pressure. At the boiling temperature, the vapor pressure becomes sufficient to overcome atmospheric pressure and lift the liquid to form bubbles inside the bulk of the substance.

Answer 3

vapor pressure is the pressure at a given temperature when liquid (or solid) state is in dynamic equilibrium with its vapor state. In other words, at a given instant the same number of molecules leave the liquid phase (turn to gas) as gas molecules that leave the vapor phase (and turn to liquid), meaning the same concentration (or partial pressure) of gas is present above the liquid state at a given temperature.

http://en.wikipedia.org/wiki/Vapor_pressure