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Q: bubbles in boiling water ( Answered 4 out of 5 stars,   0 Comments )
Question  
Subject: bubbles in boiling water
Category: Science > Chemistry
Asked by: fxfox-ga
List Price: $50.00
Posted: 14 Aug 2004 16:41 PDT
Expires: 13 Sep 2004 16:41 PDT
Question ID: 387910
When water boils, where do the little bubbles of air in the water come from?
Answer  
Subject: Re: bubbles in boiling water
Answered By: bobbie7-ga on 14 Aug 2004 20:58 PDT
Rated:4 out of 5 stars
 
Hello Fxfox,  

Below you will find information and links to websites regarding 
bubbles in boiling water.


From The International Collaborative Boiling Point Project: 

?As water boils, the water turns into steam (also known as water vapor
or water gas.)

(..) 

?First the water begins to form bubbles at the bottom near the heating
device (see if this happens for you.) Then, the bubbles begin to rise
until the bubbles begin to pop off the surface of the water and
seemingly evaporate into the air.?

Where do the bubbles come from?

?The energy from the heating device first raises the temperature of
the water. At a certain temperature, that energy is used to transform
the water from its liquid state to its gaseous state (that's when you
start seeing the bubbles form.) As the energy from the heating device
goes into heating the water, the water temperature rises.

(..)

?But at a certain temperature, the heating energy goes only to turning
the water into a gas. When that point is reached, your thermometer
will not get any higher and you will have found the boiling point of
your water.?

(..)

?As you heat up the water, you are breaking down the liquid molecule
so that it can turn into a gas. Bubbles begin to be created in the
base of the heating water first. But the pressure of the outside air
will squash those bubbles at first because they don't have enough
pressure inside them to stand up to the outside air pressure. As more
energy goes into making those bubbles though, they will begin to be
able to stand up to the outside air pressure. When they get to the
point where they can stand up to the outside air pressure, you'll see
massive bubbles coming off of your water, the temperature of your
water will top off and your boiling point will be reached.?

Stevens Institute of Technology
http://k12science.ati.stevens-tech.edu/curriculum/bp/background.html


----------------------------------------------------------------------


?Water at room temperature and normal atmospheric pressure is a
liquid. As heat is added to it, the molecules move around faster and
faster. We measure this level of energy and call that property
"temperature". As more heat is added, eventually the molecules get
energetic enough that they won't stay bound to the rest of the mass of
liquid; their 'vapor pressure' exceeds the ambient atmospheric
pressure, and bubbles
start to form.? 

Science Education Partnership
http://www.seps.org/oracle/oracle.archive/Physical_Science.Physics/2000.02/000950385832.3755.html


----------------------------------------------------------------------


Where do the bubbles come from when you boil water?

?Water is a liquid. When you heat it, it moves around a lot faster.
When the water reaches 100 degrees Celsius, it turns into a gas called
water vapour.

This gas is less dense than the water around it, so it rises to the
top. Then it escapes into the air. As more and more of the water turns
into gas, more of it disappears into the air. After a while, every
last drop of the water will be gone.

?Most of the bubbles start at the bottom, because that's where the
heat is. The more heat you apply, the more bubbles you will get. The
water is turning into a gas very quickly, and lots of bubbles form,
and all try to rise to the surface at once. They push the water out of
the way as they rise, and jump out of the surface. This is what we
call 'boiling water'?.
http://www.geocities.com/thesciencefiles/bubbles/page.html


----------------------------------------------------------------------


According to Richard Stein, Professor of Chemistry, Natural Sciences,
Germanna Community College:

?Boiling is the transition from liquid to vapor.  As the process
occurs, the liquid is trying to form a vapor - gases expand rapidly
with temperature increases so
any air that is dissolved will also expand as does the water vapor to form
bubbles in the cooler liquid as they try to escape.?

MadSci Network: Chemistry
http://www.madsci.org/posts/archives/may98/893876065.Ch.r.html


----------------------------------------------------------------------


From Ask a Scientist:

?Please tell me why and how bubbles form at the bottom of the pot when
water is heated.?

Boiling is when the liquid water converts to gaseous water.  I have
noticed that sometimes I get some small bubbles on the bottom of the
pan long before boiling
commences.  I attribute this to the change in solubility of air
(nitrogen and oxygen) in water as the temperature changes.  The
solubility of gases in water decreases as temperature rises.
Ask a Scientist 
http://www.newton.dep.anl.gov/askasci/chem99/chem99350.htm


----------------------------------------------------------------------


For example: 

?We set a pot of water on the stove and turn on the burner. As it
heats, little bubbles form along the bottom and sides of the pot.
Pretty soon they rise, get big, and make it to the surface where they
burst. Now the pot is boiling.?

(..)

Bubbles begin life as tiny air bubbles, but once they grow to visible
sizes, they are almost entirely water vapor mixed with a little air.
Water surrounding the tiny air bubbles evaporates into them, causing
them to grow.
USA Today: March 2004
http://www.usatoday.com/tech/columnist/aprilholladay/2004-03-11-wonderquest_x.htm


----------------------------------------------------------------------


The bubbles are mostly of steam trying to escape 

?If a liquid is heated continuously, vaporization takes place in all
parts of the liquid at a particular temperature. The liquid undergoes
a complete change of state into gaseous state. The process is known as
boiling.?

?Take a beaker and heat it till the water starts boiling. You will see
that bubbles start forming at around 70C. The bubbles are mostly of
steam trying to escape. When the bubbles are large enough, they come
on the surface and escape as steam. When the pressure in the bubble is
less than the atmospheric pressure, the bubbles remain inside the
liquid. When the pressure becomes greater than the atmospheric
pressure (when the bubbles coalesce to form larger bubbles) the
bubbles burst and the boiling is seen at all places in the liquid.?
http://home.att.net/~cat4a/heat-III.htm


----------------------------------------------------------------------

The bubbles that form in boiling water are air bubbles. 
?The gas bubbles that form when something boils are filled with the
gas form of whatever is boiling. In the case of water, some of the
atoms in the liquid have bounced off of each other hard enough to
break free of their attractions, forming a gas. That is why water
appears to dissappear when it boils. The gaseous form of water is
invisible, just like air, so water is not seen as it leaves from a
boiling pot.?
http://workbench.concord.org/web_content/unit1/1-17PhasesAndVolume.html


----------------------------------------------------------------------


?Water will start boiling when the kinetic energy (motion energy) of
the water molecules is great enough to enable them to break away from
each other. The water molecules will then leave the bulk of water and
exist in gaseous state.?
The Concord Consortium
http://www.science.edu.sg/ssc/detailed.jsp?artid=2661&type=6&root=5&parent=5&cat=54

----------------------------------------------------------------------


Search terms used: 
boiling water bubbles form


I hope you find this information helpful!


Best regards,
Bobbie7
fxfox-ga rated this answer:4 out of 5 stars

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