I get there’s less and less air pressure the closer you get to sea level, and therefore it requires less energy for water to boil, but how does air pressure correlate to energy? I have a tendency to think about things at the molecular level, and can’t seem to work this one out in my head.
In: Chemistry
Think of air pressure as little people pressing down on water molecules trying to leave the surface of water.was air pressure, the easier and quicker the water molecules can escape. The water requires less energy to overcome that pushing back air has.
Pressure being “worked against” is lower, less force is needed for the water vapor molecules to “leave” the pot.
There isn’t a correlation with energy. The water will boil at a lower temperature. Simplified it’s just that the air pressure that’s lower isn’t pushing as hard on the molecules, allowing them to shift phase and break the bond in the liquid easier.
If you put a cup of water in a vacuum chamber you’ll see it boil quite quickly when the pressure drops. The liquid itself will even cool down as more water evaporates. Basically the same mechanism an airconditioner used too cool.
My standard explanation of states of matter is to think of a bunch of young kids sitting on the floor in a classroom. A solid is where they’re all sitting nice and calm. Add in some energy, and they begin to jostle about a bit, which takes up more space. Maybe they’ve got enough room to move past each other to speak to their friends. This is a liquid. Add in some more energy, and occasionally one of the kids at the back will just stand up and wander about the room. This is evaporation. If there’s enough hype that one of the kids from the middle stands up and starts walking around, this is boiling. When they’re all energetic enough that they just walk about freely, you’ve got a gas.
Okay, so now let’s add in some air pressure. This is like the older kids who are standing around acting as monitors. If a kid starts to misbehave and looks like they’re evaporating, the monitor can calm them down. But if there’s too much energy and too many kids are getting hyper at once, there aren’t enough monitors to go around and the kids start to boil.
Now suppose we take away half of the monitors. This is like a lower atmospheric pressure. Since there aren’t as many monitors, it’s even easier for the kids to get too hyped up for the monitors to cope, and we reach boiling point much sooner.
The pressure is higher at sea level, lower at higher altitudes. Water boils at a lower temperature at higher altitudes, so it takes less time on the stove to get to that lower temperature, compared to a higher temperature if you were closer to sea level.
Imagine you want to jump. Unfortunately for you you have a backpack on weighing 50 kilos. This makes it pretty hard, and takes a lot of effort to do.
Now imagine that weight gets reduced to 20 kilos. It’s still pretty difficult, but way easier than before and you don’t have to put in as much energy to do it.
By going up you decrease atmospheric pressure that is “squishing” the water into its liquid state, and so it takes less energy to overcome it with heat.
The air pressure is constantly pushing down in the surface of the water.
If a water molecule breaks loose of the surface, it evaporates. The air pressure pushing down on the water prevents this from happening so easily.
If you bring the water to a near vacuum, the water will boil off without any heat at all. The temperature the water already has means the water molecules are jiggling around enough to escape the surface of the water on its own because there’s no air pressure to hold it back.
[Phase diagram](https://files.mtstatic.com/site_4334/78506/0?Expires=1722647921&Signature=pHelPE6bi3MGmUciUO64641qSpSl8~scbhojcMJ9O7sMShnSE7jV2ZGZLaTpY04SONVndj3WMwGxcDscI3jkZa~cVbTZNtym9vlnQkCfpBAkIWyVwxHcrk5-8HbhoqPFtIJdMU1-P3jBz3QUfZwpWusl5u2Gxf~fxhTA1aVeSXI_&Key-Pair-Id=APKAJ5Y6AV4GI7A555NA)
There’s *more* pressure the closer you get to sea level. So the further from sea level the air pressure goes down, the less tightly the molecules are being packed, and the lower the boiling temperature.
So the state of matter is dictated by how close them molecules are to eachother. You can force molecules closer to eachother by lowering the temperature and/or raising the pressure and vice versa.
Think of it like you (temperature) and your brother (pressure) lifting (boiling) 100Kg of water. If your brother just stands there doing nothing (pressure remains at 1 atm) then you will have to do all the lifting (temperature has to raise to 100C). If your brother helps you (if pressure drops below 1 atm) then you no longer have to do all the lifting (temperature no longer has to go to 100C).
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