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Boiling at Room Temperature
Name: Devin
Status: student
Age: 7
Location: N/A
Country: N/A
Date: Around 1999
Question:
Can water boil at room temperature? Mom says that you
can do it if you put the container of water in a vacuum chamber.
Replies:
Dear Devin,
Yes, your mom is right. Water can boil at room temperature if the
pressure is reduced enough (a vacuum means zero pressure).
In general as the pressure decreases, so does the temperature
required to boil a liquid. The boiling point at the top of
a mountain is lower than it is at the bottom, because the
air pressure is lower at the top.
I used to live in Colorado, and when I was there I had to steep
my teabag to make tea longer than here in NEw York. This is because
boiling water in Colorado, which is about a mile high in elevation,
is cooler than boiling water in New York, which is at sea level.
Thanks for your question, hope this helps you understand
boiling a little better.
Best wishes,
Prof. Topper
Mom is right. In fact, when you do this, the water will boil and freeze at
the same time.
The reason is that at room temperature, water molecules are constantly
going into the air as vapor and moving back into the liquid water. When
you heat water, you are making the vapor that comes off the water have a
higher pressure. When the pressure gets as high as the pressure of the
surrounding air, bubbles of vapor can form inside the liquid and push
against the air. When this happens, the liquid boils. If you remove the
air and water vapor in a vacuum chamber, water vapor can't go back into the
liquid. In fact, the vapor going off from the liquid will have enough
pressure to actually make bubbles in the liquid.
That's why water will boil in a vacuum chamber. I also told you it will
freeze at the same time. Why is this? It turns out that water molecules
like to be next to each other in the liquid. It takes energy to move them
into the vapor. When water molecules are moving back and forth between the
liquid and vapor, the energy that is taken from the liquid to put molecules
into the vapor is replaced by the energy returned when molecules move from
the vapor into the liquid. In the vacuum chamber, though, the vapor is
taken away, so none of the energy is returned to the water. As the water
loses energy, it gets colder and finally freezes.
Richard Barrans Jr., Ph.D.
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Update: June 2012
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