Water At 100 Degrees

[joggerjayne]

There's an advert on the telly at the mo for one of these instant boiling tap things.

It's called Quooker.

The advert says it delivers water at 100 degrees.

A big 100 comes up on the screen.

But if it was 100 degrees, wouldn't it just be vapour coming out of the tap?

Any science people to clarify please?

[sandyRoe]

In the pipes and tap could it evaporate?

[bibblebub]

not if 100 Fahrenheit

[jno]

let me just ask Dr Fahrenheit...

He says it depends where you are. Atmospheric pressure/elevation makes a difference.

[rockyracoon]

No idea how it works but I really want one, I think a couple of members on here are have them.

[jim360]

Not necessarily. Boiling points primarily depend on pressure. So if the water were highly pressurised as it left the tap it might not boil so easily.

Moreover, when you heat water to 100 degrees Celsius it doesn't immediately turn into vapour -- it's just that at this point the pressure if the water (water vapour) is enough to let it escape more readily, so that the liquid will start turning into vapour -- but you need to pump in yet more energy to change the water from liquid to gas.

So, in short, no it wouldn't necessarily come out as just vapour.

[jno]

that's your cue to go out and buy one, then...

[Prudie]

Well if boiling kettles only gave out steam you could never make tea! We have them at work, only downside is they spatter so have to be very careful. I'd still rather use a kettle.

[joggerjayne]

So it's a "maybe"??

[Peter Pedant]

.

Jay Jay - people have not been very helpful.
The key words are change of state.

At 100'C (and 1 atm but none of us are up Everest this evg)
you can have water at 100'C and steam at 100'C

and similarly for the change of state from water to ice - both can exist at 0'C

You have to add energy to make water evaporate at 100'C
and you have to take energy away to get warer to turn to ice.

So steam at 100'C is hotter (=has more energy) than water at 100'C
( and ice is colder etc)

now you may ask yourself - if I get steam 100'C and turn it towater at 100'C, can I or would I be able to get work out of it.
and the answer is yes this is the start of thermodynamics

[joggerjayne]

Thank you, Peepee

[joggerjayne]

(and everyone else)

[Old_Geezer]

Water can be liquid or gas at 100ºC. One simply needs to put more energy in to change from one state to the other. So no, I can't see steam coming out.

These things are not cheap. I decided they were asking too much when I considered one.

[theprof]

MrsProf recently had one of these fitted in our kitchen - I should have guessed what would happen when she followed my PA into the lab kitchen to make a coffee and saw one for herself!

Anyway, I can confirm that water does come out of the tap at as close to 100 degrees C as makes no difference for domestic use. I've bunged a specialised standardised thermometer beneath the stream and it comes up with a consistent reading of 99.99999998 C which you can safely regard as being the closest to boiling water as you'll ever actually need.

Before I saw the lab Quooker working, I thought that if this device didn't serve as a severe scalding hazard, nothing would. However, all the models release the water as a spray from the outlet rather than what you are accustomed to from a tap. The flow mechanism is completely childproof.

The tank beneath the sink holds 3 litres of water and uses about 10W of power in standby mode. The heater itself is rated at about 1600W.

The bad news is that although Quooker and currently running a free installation scheme, the complete set-up will not give you much change from around £900.

All the same, it does make lovely tea first thing in the morning!

[theprof]

Methyl is absolutely right. Tap water has a number of contaminants which affect it's boiling point albeit minutely. This coupled with heat losses during the transit of water from the tank to the tap means that the water cannot be precisely 100 degrees C so the Quooker manufacturers are being slightly economical with the truth.

[Hopkirk]

I bet if you fitted one in our house, it would scale and be useless in a matter of weeks.

[Hopkirk]

- scale up -

[jake-the-peg]

This is a common misconception and comes up all the time and it's a subtle inaccuracy in how people understand what boiling point means.

Old_geezer's on the nail - water can be liquid or vapour at 100 degrees

Think of it this way - 100 degrees is the maximum temperature water can be at in liquid form (at atmospheric pressure)

If you try and heat water past this it will just speed up the rate at which it turns to gas.