[neilep (OP)]

When boiling water...bubbles appear ?...what is in the bubbles ?

Also...does this mean that when the bubble floats up and bursts that the water has changed ?.....because there is less of that gas now in the water  !!

Does the gas get replaced in the water somehow ?...if so ....how so ?

[_Stefan_]

I thought it was Dihydrogen Monoxide gas. The water molecules get hot enough to break their hydrogen bonds and turn into gas, at which point they float to the surface in bubbles and pop, thereby escaping into the atmosphere.

I don't think the water left behind has changed, except that there is less of it due to evaporation and it might also be more concentrated with salts etc.

[_Stefan_]

Oh, also, warm/hot water is much less oxygenated than cooler water.

[BillJx]

I thought it was Dihydrogen Monoxide gas. The water molecules get hot enough to break their hydrogen bonds and turn into gas, at which point they float to the surface in bubbles and pop, thereby escaping into the atmosphere.

I don't think the water left behind has changed, except that there is less of it due to evaporation and it might also be more concentrated with salts etc.

Yes, it's steam.


They don't break their hydrogen bonds; steam is just water molecules that have decided to dance independently instead of en masse. 
  The molecular behaviour of water is actually quite interesting.  Water is a polar compound (google it) which makes the molecules stick together for the same reason balloons can stick to the wall.  It's also what makes your tea cling to the side of the spout when you're trying to pour.  When water gets hot enough, the molecules are bouncing around with enough energy to overcome this attraction and break away from one another.

I'm not a scientist by the way, just a 2nd class steam engineer who boils water for a living.  About a million pounds of it per hour.

[neilep (OP)]

THANK YOU STEFAN for you wise words and also THANK YOU BILLJX for your excellent post too !!


So....Bill....are you boiling potatoes en-masse or is it some big mega industrial type thing you're doing all this for ?

[Bored chemist]

"When water gets hot enough, the molecules are bouncing around with enough energy to overcome this attraction and break away from one another."
Quite right.
"They don't break their hydrogen bonds"
Not quite so right; the attraction between the water molecules is cause by hydrogen bonds.

I can't help wondering how much water you need to boil in an hour to get promoted to a 1st class steam engineer. :-)

[_Stefan_]

"They don't break their hydrogen bonds"
Not quite so right; the attraction between the water molecules is cause by hydrogen bonds.

Thanks for backing me up BC.

[BillJx]

"They don't break their hydrogen bonds"
Not quite so right; the attraction between the water molecules is cause by hydrogen bonds.

Thanks for backing me up BC.

Sorry, terminology problem. I've always called it an electrostatic bond.  Thanks for the correction.
 There's a reasonable graphic here: http://www.visionlearning.com/library/module_viewer.php?mid=57

[Batroost]

All true. But you also need to remember that Henry's law comes into play reducing the solubility of gases as the water heats-up. The upshot is that as the water approaches boiling point all of the O₂, N₂, CO₂ (etc) are forced out of the liquid. The bubbles you first see on the bottom of a pan of water as you heat it are predominently dissolved gases coming out of solution and not steam. The steam bubbles only appear when areas of the liquid are sustained at boiling point.

If you want to see a demonstration of this, boil some water and let it cool for a little while - preferably closely covered, say in a lidded container filled to the brim, so as to prevent lots of gas being re-absorbed by the water. Then boil it a second time and you'll see far fewer bubbles on the way to bulk boiling.

Regards,

Batroost (from a place that makes 2 tonnes of steam a second - what's that in pounds per hour?).