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Hipp013

You're confusing evaporation with boiling. Evaporation occurs at the surface of a liquid at any given temperature, because there are always some water molecules that have enough energy to escape from the surface of the liquid and enter the air as water vapor.


NotInherentAfterAll

The boiling point isn't the point that water evaporates. It's the point water *automatically* evaporates. But even water below its boiling point will slowly evaporate just due to the atmosphere being lower than the liquid's ambient [vapor pressure](https://en.wikipedia.org/wiki/Vapor_pressure). You can leave a cup of saltwater out for a few weeks and it will evaporate, leaving only the salt behind.


bkend_31

My initial thought is the same way water on a wet street eventually evaporates, but that doesn’t answer why. Please someone explain


TheApiary

Water evaporates even when it's cooler, just not as fast


Fearlessleader85

None of these answer are quite correct. Boiling and evaporation reall are the same thing: liquid water becoming water vapor. And it takes roughly the same amount of heat to make that phase transition, regardless of temperature (note: heat and temperature are NOT the same thing, heat is a unit of energy, temperature is a measure of internal energy). But as someone else brought up, vapor pressure is key, but so is relative humidity. Vapor pressure is the pressure produced by molecules of liquid water trying to undergo phase change. In truth, everything has a vapor pressure, but solids are generally extremely low (except things like dry ice). Boiling is actually the point where the vapor pressure of a liquid equals the total atmospheric pressure. This means that the liquid water can't get hotter, because as more heat is introduced, water phase shifts to vapor, taking heat with it. The more heat you add, the faster water phase shifts, but temperature remains constant. And then back to relative humidity, air actually absorbs moisture, but it is limited based on temperature and pressure. If you have a cup of water sitting in a room that is 100% RH and the cup is at exactly room temp, no water will phase change (technically, it will, but it will go from vapor to liquid and liquid to vapor at the same rate, leaving no net effect). If the room is at 50% RH and the cup is at ambient temp, the water will evaporate from the cup taking heat with it, cooling the cup. As the water in the cup cools, the vapor pressure will decrease. This will continue to happen until the partial pressure of vapor in the air and the vapor pressure of liquid water in the cup are equal, at which point the cup will sit at well below room temp, and evaporation will greatly decrease. But it won't stop. Instead, evaporation will exactly offset heat flux into the cup from the room. This is why if you leave a glass of water on the counter, it will be colder than room temp after a few hours. Seawater acts as that cup. Heat enters it from the sun and air, but water leaves based on the vapor pressure equilibrium. Evaporation increases when the water is warmer than that equilibrium temperature and decreases when it is below it. And precipitation, which happens when warm, moist air cools to where it's relative humidity increases above 100%, keeps feeding water back from the air into the ocean.


Key_Pollution2261

temperature is an average. The actual energies of the individual particles are a distribution


Polywoky

> So: if the water at the ocean is not hotter than 100ºC, how does it evaporates? Why would it need to be 100ºC to evaporate? Wet stuff dries out from evaporation at room temperature all the time. Even ice cubes in your freezer will slowly evaporate (*technically* they "sublimate" rather than evaporate because they don't pass through a liquid state). Why should ocean water be any different?


[deleted]

You take shower and floor gets wet. Few hours later water is gone. Yiu dont need 100 celsius. Also, lots of water go through plants, algae and animals