So, I wondered why water turns into gas at room temperature. Apparently, it has to do with uneven kinetic energy through a body of water.
So, if we had very tiny, impossibly tiny thermometers and we put them at the surface of a body of water at room temperature, would the thermometers read it as being around 100 degrees Celsius?
If we put impossibly tiny cameras, would they show water boiling on the surface just a larger body boils on a stove at 100 degrees?
Why is the kinetic energy distribution more uneven in water than other materials? Why does the heat concentrate on the surface rather than other areas?
Is it a property of all liquids at a given temperature to ever so slightly boil on their surface area?
Temperature is a measure of the average kinetic energy of the molecules in the water. Like any average, it has a wide range of individual values. When a molecule at the water’s surface has a kinetic energy great enough to allow it to break the surface tension holding it it can escape the liquid and turn into vapor.
You can do a Boltzmann distribution to find out what fraction of the molecules have enough kinetic energy to vaporize. The rate of evaporation will vary of course with temperature, the surface tension of the liquid, surface area in contact with the atmosphere, humidity in the air, because water molecules in the gas phase exist in equilibrium and can go back into the liquid phase.
Water (and other fluids) boil when the ambient pressure is less than the vapor pressure of the fluid. At sea level standard pressure (101.3 kPa or 14.7 psia) the temperate at which a body of pure water will boil is 100 °C (212 °F). However, because air will naturally carry a certain amount of water vapor depending on temperature and pressure, a body of water with an free surface will release individual molecules until the system achieves equilibrium even at well below the boiling point temperature; this is due to the energy density difference between air and water and the tendency for individual molecules to have a kinetic energy along a distribution, with some significantly above the mean. The addition of an energy source, such as sunlight, which will locally heat the water exacerbates this. Water (of all “normal” liquids) is particularly prone to this because of it’s low molecular weight, but all fluids will evaporate to some degree at temperatures below the boiling point; the same is true of (most) solids which will sublimate individual molecules or atoms.
It is an error to think of individual molecules or even small bodies of discretely accounted particles as having a temperature or pressure, as these are not measures of any absolute property but instead are aggregate measurements resulting from the average kinetic energy and momentum of the fluid. Because of the statistical nature of energy distribution in a large body of particles, some will naturally exceed the cohesive or ionization energy and become vapor.
A lot of misconceptions in your OP. So let me try to clear up a few:
1> Think of the top layer of a liquid : some molecules will escape the surface and some molecules from the air on top will fall back into the liquid.
2> If you have a closed cylinder half filled with water and half with air (Standing vertically), molecules will escape the water surface and molecules will drop out of the air into the water. At a certain point - this phenomenon will reach an dynamic equilibrium - that is the number of molecules leaving the water will equal the number of molecules condensing back into the water.
3> What percent of water molecules in the air above the water in the cylinder ends up at equilibrium is termed as vapor pressure. You can instinctively see that - if there was no air , then it will be pure water vapor and if there was a lot of air - then enough water molecules will end up in air - so that the total count of molecules is the same in either case. So the concentration (percent) of water molecules times the total pressure gives the partial pressure of water in the air which is also the same as vapor pressure when the system is in equilibrium.
4> If the cylinder was open - then the equilibrium is never reached and water keeps evaporating. (molecules keep leaving the surface).
5> Vapor pressure is only a function of temperature - you can instinctively see this since number of molecules leaving the water surface is a function of temperature (energy)
6> If you were to apply partial vacuum to the top of the cylinder - molecules will start leaving the water surface in bigger numbers and will stop only when the partial pressure again matches the vapor pressure. If too much vacuum is applied at a given temperature, the entire liquid will vaporize but not be able to meet the partial pressure (boiling).
7> If you increase the temperature - there will come a point where the vapor pressure equals the air pressure - this is the boiling temperature.
Wikipedia’s Probability Density Function page has an image at the top that might be helpful. That could be the graph for the distribution of energy in molecules of water at a given temperature, with energy along the horizontal axis. At this temperature, maybe 4 sigma on the horizontal axis is the energy needed for a molecule to escape from the liquid into the atmosphere. Most molecules don’t have enough energy to escape, but a few far to the right can.
Raising the temperature, the whole curve slides to the right, so maybe 3 sigma corresponds to enough energy to escape. Now more molecules will have enough energy, and the rate of evaporation will increase.
Most of the important points about why evaporation has occurs has been covered above: it’s because a small fraction of the molecules have kinetic energies well above average, and those are the ones that can escape.
Also note that since the molecules with the highest kinetic energies escape from the liquid, and temperature is a measure of the average kinetic energy (KE) per molecule, the net result is that evaporation actually serves to cool the liquid. (As an analogy, if the wealthiest 1% of Americans all decided to move to Canada, the average net worth of a U.S. citizen would decrease.) This is one of the techniques that is used to get ultra-cold temperatures in the laboratory.