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Q. Take an open container of water up high enough and it will boil away. . .



 
 
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  #1  
Old August 11th 03, 12:08 AM
Jim
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Posts: n/a
Default Q. Take an open container of water up high enough and it will boil away. . .

Hi.

I understand if an open container of water is taken up to altitude
high enough, that it will boil away.

I take that to indicate when water is brought to a boil on our stove,
at sea level, that the heat actually activates or motivates the water
molecules to begin going crazy and rubbing against each other, and
creating the vapor which must escape.

But if one were to take that open, cold pot of watet to a given point
above the earth's atmosphere, would the water get hot, as it would on
the stove, while it boils away?

Thanks,
Jim
  #2  
Old August 11th 03, 01:21 AM
Logic
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Posts: n/a
Default Q. Take an open container of water up high enough and it will boil away. . .


"Jim" wrote in message
...
Hi.

I understand if an open container of water is taken up to altitude
high enough, that it will boil away.

I take that to indicate when water is brought to a boil on our stove,
at sea level, that the heat actually activates or motivates the water
molecules to begin going crazy and rubbing against each other, and
creating the vapor which must escape.

But if one were to take that open, cold pot of watet to a given point
above the earth's atmosphere, would the water get hot, as it would on
the stove, while it boils away?

Thanks,
Jim


Anyone? Am I right in saying that though the water "boils" it does not
however increase in temperature? And is this srictly on-topic?


  #3  
Old August 11th 03, 01:21 AM
Logic
external usenet poster
 
Posts: n/a
Default Q. Take an open container of water up high enough and it will boil away. . .


"Jim" wrote in message
...
Hi.

I understand if an open container of water is taken up to altitude
high enough, that it will boil away.

I take that to indicate when water is brought to a boil on our stove,
at sea level, that the heat actually activates or motivates the water
molecules to begin going crazy and rubbing against each other, and
creating the vapor which must escape.

But if one were to take that open, cold pot of watet to a given point
above the earth's atmosphere, would the water get hot, as it would on
the stove, while it boils away?

Thanks,
Jim


Anyone? Am I right in saying that though the water "boils" it does not
however increase in temperature? And is this srictly on-topic?


  #4  
Old August 11th 03, 01:40 AM
Sohail
external usenet poster
 
Posts: n/a
Default Q. Take an open container of water up high enough and it will boil away. . .

my probably flawed guess:

it's not the temperature per se that causes the water to boil. It is
actually the vapour energy of the water molecules vs the atmospheric
pressure. At sea level, it gets converted to gas through high temperatures
b/c we have higher pressure down here and thus the water molecules need more
energy to escape. Remember that water molecules always have kinetic energy
(which is probably what i'm referring to as vapour energy) and pressure of a
container always works against this energy.

just my $0.02 worth of what i remember from high school. Come to think of
it, thats probably all its worth

"Jim" wrote in message
...
Hi.

I understand if an open container of water is taken up to altitude
high enough, that it will boil away.

I take that to indicate when water is brought to a boil on our stove,
at sea level, that the heat actually activates or motivates the water
molecules to begin going crazy and rubbing against each other, and
creating the vapor which must escape.

But if one were to take that open, cold pot of watet to a given point
above the earth's atmosphere, would the water get hot, as it would on
the stove, while it boils away?

Thanks,
Jim


  #5  
Old August 11th 03, 01:40 AM
Sohail
external usenet poster
 
Posts: n/a
Default Q. Take an open container of water up high enough and it will boil away. . .

my probably flawed guess:

it's not the temperature per se that causes the water to boil. It is
actually the vapour energy of the water molecules vs the atmospheric
pressure. At sea level, it gets converted to gas through high temperatures
b/c we have higher pressure down here and thus the water molecules need more
energy to escape. Remember that water molecules always have kinetic energy
(which is probably what i'm referring to as vapour energy) and pressure of a
container always works against this energy.

just my $0.02 worth of what i remember from high school. Come to think of
it, thats probably all its worth

"Jim" wrote in message
...
Hi.

I understand if an open container of water is taken up to altitude
high enough, that it will boil away.

I take that to indicate when water is brought to a boil on our stove,
at sea level, that the heat actually activates or motivates the water
molecules to begin going crazy and rubbing against each other, and
creating the vapor which must escape.

But if one were to take that open, cold pot of watet to a given point
above the earth's atmosphere, would the water get hot, as it would on
the stove, while it boils away?

Thanks,
Jim


  #6  
Old August 11th 03, 02:26 AM
Odysseus
external usenet poster
 
Posts: n/a
Default Q. Take an open container of water up high enough and it will boilaway. . .

Jim wrote:

I understand if an open container of water is taken up to altitude
high enough, that it will boil away.

I take that to indicate when water is brought to a boil on our stove,
at sea level, that the heat actually activates or motivates the water
molecules to begin going crazy and rubbing against each other, and
creating the vapor which must escape.

More or less. The temperature indicates the average kinetic energy of
the water molecules. But in order for the phase to change from liquid
to vapour, additional heat is required. This is evidenced by the fact
that as the pot is heated the water in it will reach 100°C quite a
while before enough heat has been added to bring it to a full boil.

In any open container of liquid there is an equilibrium between the
rate at which molecules in the liquid phase evaporate from the
surface and that at which vapour from the air condenses back into the
liquid. Even at room temperature, if the air is dry enough, and
especially if there's a wind to carry vapour away, a glass of water
will evaporate. OTOH the water in a sealed pressure-cooker doesn't
boil easily because of the high pressure inside, and can be brought
to a temperature much higher than its normal boiling point while
remaining in the liquid state.

At any given temperature water -- and even ice -- has a
characteristic "vapour pressure"; as long as the partial pressure of
water vapour above the liquid is lower than the vapour pressure, more
molecules will be lost to evaporation than are gained by
condensation, and _vice versa_. We say a liquid is at its "boiling
point" when its vapour pressure equals the atmospheric pressure.

But if one were to take that open, cold pot of watet to a given point
above the earth's atmosphere, would the water get hot, as it would on
the stove, while it boils away?

No. By taking the pot high into the atmosphere you're lowering the
pressure; where this is lower than the vapour pressure appropriate to
the water's temperature, boiling will take place. Since the escaping
vapour carries heat away with it, the temperature of the water
remaining in the pot will actually drop; the same principle underlies
the cooling power of any refrigerator or air conditioner, except that
water (which is extraordinarily resistant to vaporization for its
molecular weight) is much less suitable for the purpose than Freon
and other such substances.

--
Odysseus
  #7  
Old August 11th 03, 02:26 AM
Odysseus
external usenet poster
 
Posts: n/a
Default Q. Take an open container of water up high enough and it will boilaway. . .

Jim wrote:

I understand if an open container of water is taken up to altitude
high enough, that it will boil away.

I take that to indicate when water is brought to a boil on our stove,
at sea level, that the heat actually activates or motivates the water
molecules to begin going crazy and rubbing against each other, and
creating the vapor which must escape.

More or less. The temperature indicates the average kinetic energy of
the water molecules. But in order for the phase to change from liquid
to vapour, additional heat is required. This is evidenced by the fact
that as the pot is heated the water in it will reach 100°C quite a
while before enough heat has been added to bring it to a full boil.

In any open container of liquid there is an equilibrium between the
rate at which molecules in the liquid phase evaporate from the
surface and that at which vapour from the air condenses back into the
liquid. Even at room temperature, if the air is dry enough, and
especially if there's a wind to carry vapour away, a glass of water
will evaporate. OTOH the water in a sealed pressure-cooker doesn't
boil easily because of the high pressure inside, and can be brought
to a temperature much higher than its normal boiling point while
remaining in the liquid state.

At any given temperature water -- and even ice -- has a
characteristic "vapour pressure"; as long as the partial pressure of
water vapour above the liquid is lower than the vapour pressure, more
molecules will be lost to evaporation than are gained by
condensation, and _vice versa_. We say a liquid is at its "boiling
point" when its vapour pressure equals the atmospheric pressure.

But if one were to take that open, cold pot of watet to a given point
above the earth's atmosphere, would the water get hot, as it would on
the stove, while it boils away?

No. By taking the pot high into the atmosphere you're lowering the
pressure; where this is lower than the vapour pressure appropriate to
the water's temperature, boiling will take place. Since the escaping
vapour carries heat away with it, the temperature of the water
remaining in the pot will actually drop; the same principle underlies
the cooling power of any refrigerator or air conditioner, except that
water (which is extraordinarily resistant to vaporization for its
molecular weight) is much less suitable for the purpose than Freon
and other such substances.

--
Odysseus
  #8  
Old August 11th 03, 01:02 PM
Ron Miller
external usenet poster
 
Posts: n/a
Default


"Jim" wrote in message
...
Hi.

I understand if an open container of water is taken up to altitude
high enough, that it will boil away.

I take that to indicate when water is brought to a boil on our stove,
at sea level, that the heat actually activates or motivates the water
molecules to begin going crazy and rubbing against each other, and
creating the vapor which must escape.

But if one were to take that open, cold pot of watet to a given point
above the earth's atmosphere, would the water get hot, as it would on
the stove, while it boils away?


No: it will not get hot. What happens is that the lower the pressure is, the
less heat is needed to make the water boil. At some point you will reach a
pressure (or lack of it) where water will boil at room temperature. In other
words, the boiling point of water is 212 degrees F at sea level. The higher
you go, the lower the boiling point is. At an altitude where the boiling
point is 98 degrees, your own body heat is sufficient to cause water to
boil---and your own blood, too, for that matter.

R


  #9  
Old August 23rd 03, 12:13 PM
Painius
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Posts: n/a
Default

"Logic" wrote in message...
...

"Jim" wrote in message
...

Hi.

I understand if an open container of water is taken up to altitude
high enough, that it will boil away.

I take that to indicate when water is brought to a boil on our stove,
at sea level, that the heat actually activates or motivates the water
molecules to begin going crazy and rubbing against each other, and
creating the vapor which must escape.

But if one were to take that open, cold pot of watet to a given point
above the earth's atmosphere, would the water get hot, as it would on
the stove, while it boils away?

Thanks,
Jim


Anyone? Am I right in saying that though the water "boils" it does not
however increase in temperature? And is this srictly on-topic?


'Lo Logic 'n Jim --

Others have responded about the altitude effect on water. As far
as the on-topic question is concerned, its application may become
clear when one considers the effects of reduced pressure on the
circulatory systems of astronauts.

hth

happy days and...
starry starry nights!

--
Sweet home, oh Precious Earth,
The ONLY home we know,
Tell us what you need of worth,
And we can make it so.

Do you want our hearts to beat
And thrive within your air?
Then teach us what we know we need
So we can learn to care.

Paine Ellsworth


 




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