#1
OK, so my clas did an experiment where, water would be boiled in a beaker, and once it reached boiling pont, we would stoper the beaker, flip it upside down and put it under a tap with cold water. when we did that, the water started boiling again, at a lower temperature. I am supposed to explain what caused this, i know, it has to do with the low pressure to high temperature, but i cant explain it well, i need to include what the atoms are doing exactly . If someone could thatd be great. Thaaanks.
Last edited by death_rider at Oct 2, 2007,
#5
heat doesnt boil water. pressure does. heat is just the easiest way to achieve the required pressure normally. but since the water was boiling, there was alot of water vapor evaporated into the air inside the beaker. When you cut off the humid airs escape, and cooled it, the water vapor begins expanding. since theres nowhere for the water vapor to expand into, pressure builds up inside, causing the water to begin boiling again.
ehh
#6
the atoms are breaking apart when its boiling, and the atoms are being released as it steams, and when stoppered, the atoms can't go anywhere, so they fly around like crazy, and when put under cold water begin to reform in a backwards sort of way, meaning that it is boiling at a weaker temperature........i think....not sure
#7
water boils at lower temps at LOWER pressure, not higher... increasing the pressure of water will not boil it... decreasing the pressure will.

I've seen water boil at room temperature, by putting it in a vacuum atmosphere... it's pretty cool.

It's probably the opposite effect... chances are when you stopper it off, and then cool it down, it cools down the gasses which were trapped inside the beaker, which causes a vacuum, since pressure and temperature have an direct relationship... (aka increase in temp of a gas causes increase in pressure at constant volume, and vice versa) which allows for the water to boil again.

Any chance you've been studying the ideal gas law lately?
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Last edited by Musicman48858 at Oct 2, 2007,
#9
Quote by skaguitarist53
heat doesnt boil water. pressure does. heat is just the easiest way to achieve the required pressure normally. but since the water was boiling, there was alot of water vapor evaporated into the air inside the beaker. When you cut off the humid airs escape, and cooled it, the water vapor begins expanding. since theres nowhere for the water vapor to expand into, pressure builds up inside, causing the water to begin boiling again.


Alright dude, thanks, makes sense to me too!

One more question though, is it low pressure when there is the higher temperature or lower?
#12
you are evaporating water so when you stopper it it is mostly water vapor and liquid water, when you cool it down with the water the water vapor condensates and the air pressure inside the beaker decreases.... if you look at the phase diagram of water it shows that when pressure decreases, the boiling point decreases
#14
Quote by death_rider
Alright dude, thanks, makes sense to me too!

One more question though, is it low pressure when there is the higher temperature or lower?


his answer is wrong... read mine and AcsticRckr89's.... i'm not trying to be hard on him... I just want you to have the right answer...

if you want a reason to trust me... I'm a chemistry grad student.
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#15
Think of it like this. In a vacuum (Low pressure), it's gonna be pulling (Vacuums...) on the molecules with enough force to overcome the dipole dipole forces. So. Low pressure = lower boiling temp.

Feel free to correct me if I'm wrong guys.
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#16
Quote by abcdboy
Think of it like this. In a vacuum (Low pressure), it's gonna be pulling (Vacuums...) on the molecules with enough force to overcome the dipole dipole forces. So. Low pressure = lower boiling temp.

Feel free to correct me if I'm wrong guys.


kind of an oversimplification... but it's not bad...
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#17
Everybody talking about pressure has it right. When you boil it first, you've got the water under standard pressure. When you run it under cold water, the water vapor exerts less pressure on the liquid water and the liquid water can boil again.

Studying the gas laws, eh?
#18
Quote by Musicman48858
his answer is wrong... read mine and AcsticRckr89's.... i'm not trying to be hard on him... I just want you to have the right answer...

if you want a reason to trust me... I'm a chemistry grad student.


okay, ill take ur word for it, but the only hting is, with ur answer, i havent talked about vaccums in class yet, im supposed to explain just with what the atoms are doing. but thatnks for ur input so far, im geting more of an understanding then before
#19
Quote by death_rider
okay, ill take ur word for it, but the only hting is, with ur answer, i havent talked about vaccums in class yet, im supposed to explain just with what the atoms are doing. but thatnks for ur input so far, im geting more of an understanding then before

Oh, no no. Vacuums was just an example. Cause vacuum cleaners suck...so...low pressure. Bad example I guess. My bad.

But yeah, important things to mention are dipole dipole forces. The molecules (not atoms...) are overcoming them.

Again, correct me if I'm wrong.
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#20
Quote by Musicman48858
his answer is wrong... read mine and AcsticRckr89's.... i'm not trying to be hard on him... I just want you to have the right answer...

if you want a reason to trust me... I'm a chemistry grad student.

Anyone that knows how to make meth gets an A in my book
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#21
just to clarify a little... by "vacuum" i mean a decrease in pressure. This allows the hydrogen bonds between the water to break easier... and thus boil at a lower temperature
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