Like if I spill water and it’s dry when I come back in a couple hours how did it do that without getting up to its boiling temp?
Is it the same type of thing like when my hair is wet and it’s in the process of drying? Because it isn’t at the 212° F or I’d feel it, right?
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Temperature is a measure of the average kinetic energy of the particles in a substance. The boiling point is when the average particle has enough kinetic energy to break free of the intermolecular forces that hold it in the liquid. Because an average is being taken, temperatures below the boiling point can still allow the particles at the energetic end of the bell curve to escape.
When a puddle of water is left in the sun, the entire puddle will not reach boiling point, but the particles on the surface will absorb more heat than the average particle in the puddle and evaporate. Then the next layer of particles become the surface and this repeats until the puddle evaporates completely without ever raising the average energy to the boiling point.
Water and other liquids can evaporate at just about any temperature. Over time, individual particles of that puddle might heat up, and so gain more movement. It does not gain as much movement as boiling water, but some movement just the same. This movement can cause that particle to separate from the main body of the puddle. When it does so, it loses a lot weight and can be less dense than air, and so floats away. So, puddle evaporation is basically when the puddle slowly breaks away, particle by particle.
Water evaporates because individual molecules acquire enough speed to break free from the attractive forces of the collection of molecules that form the liquid. At any given moment they move at a range of random speeds. Collisions make some of them faster and others slower. With rising temperature the average speed increases and evaporation is more intense. Once the surrounding air already contains water vapor, some of it rejoins the liquid and eventually an equilibrium is reached when no more net evaporation occurs.
Boiling happens when the liquid has enough energy to be forced to take a gaseous form. This transition cools it down, and more heat is required to keep it boiling.
As long as there’s less water in the air than there is in the water it will move to the air, just much more slowly. Biking temp is the temperature that forces water into a vapor gas firm that mixes with air readily. But water can dissolve ivy air at a wide range of temperature. Pressure has a lot to do with it to. The lower the air pressure the more easily water can dissolve into it. That’s why cooking instructions on food boxes have different times for high elevation. Ice can evaporate in an action called sublimation.
water evaporates all the time. Boiling is just the point when it evaporates so fast it can form bubbles
Water is made up of countless molecules.
Each one is moving around, each one has it’s own speed and direction. The temperature from a thermometer is simply an *average* for all the particles hitting it.
Some will be going faster, some will be going slower. And when they hit things they transfer the energy. Two slow ones might hit a third in quick succession. This third atom would then fly off at high speeds from the “one two punch” of the impact.
What this means is that there is some small fraction of a body of water that is traveling at high speeds (and thus “hot”) and capable of escaping a puddle entirely, then free to roam as a gas.
The remainder are cooler now, but pick up energy from the air, the light, the ground, and warm up a bit. Again some are going fast enough to flee….and these hot atoms leave.
The rest are ‘cold’ but pick up energy… and so on.
The hotter a puddle of water is, the larger the fraction of “hot enough” water capable of becoming a gas.
This goes the other way around too. Gaseous water in the air has some molecules that are on the slow side. When they collide with a puddle they may stick, and condense. This is how puddles and droplets can form and grow rather than evaporate.
In reality you always have some molecules slowing and condensing while entirely different ones get a kick, speed up and evaporate. If the puddle grows or shrinks is really a matter of the rates of these two processes, which is based on the *average* temperature.
Something you have to understand is that “evaporate” and “boil” are not the same thing.
Fluids can be thought of as like a bunch of tiny marbles sloshing around in a huge bowl, like a mosh pit. They can flow past one another and bounce around all they like, but they’re contained by the walls of the bowl. But the top of the bowl isn’t closed–it’s open. All the marbles need is enough speed to fly out of the bowl and not come back. With just the right series of lucky ricochets off of other marbles, one marble can occasionally get knocked with enough speed to fly out of the bowl. That’s essentially what evaporation is.
When a marble does get knocked out of the bowl like this, it necessarily has to do it at the expense of the marbles it knocked into just before it peaced out. Those marbles are now moving slower than they were before. The average energy of all the marbles in the bowl combined has thus gone down with the stray marble flying off.
Since temperature is just the average speed of all the marbles in the bowl (and also, the vibrations of the bowl itself, which will help keep the marbles jostling), and losing a marble makes the total energy go down, the temperature has also decreased. This is why a damp towel feels cool to the touch, or why you feel so cold when you step out of the shower. Water evaporating off of you is stealing your heat away. This is also how sweating keeps you cool.
Water, and any other fluid for that matter, can evaporate an essentially any temperature. Particles just need that lucky kick to get away. The colder the fluid is, the lower the chances this will happen, of course, since all the marbles that are there to ricochet off of will be moving slower overall. So warmer fluids will evaporate faster than cooler ones.
“Boiling” is the point where *all* the particles in the fluid are going fast enough that *all* of them can escape without needing a boost from a lucky ricochet. It’s not the point where evaporation starts, it’s the point where evaporation *must* happen. So, a fluid cannot get hotter than its boiling point. Any extra energy you dump into the fluid to make it warmer only makes it evaporate faster.
Imaging a border between water and air. Water contains 99,…% of water molecules and some gases. Air contains different gases and some molecules of water. This border is transparent. Molecules continuously go to and fro that border. The main direction is from higher concentration to lower. There are several factors which affect this movement but on the ELI5 level water molecules mainly continuously jump into air.
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