boiling water

  • Posted by a hidden member.
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    Mar 17, 2015 6:26 PM GMT
    I was having a discussion with friends. We were discussing the fascinating topic of boiling water.

    So here's the question: you're boiling a pot of water; you can boil it with a lid on the pot or with no lid; does the water come to a boil:

    A. faster with a lid on the pot

    B. faster with no lid on the pot

    C. same amount of time with or without a lid on the pot
  • Posted by a hidden member.
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    Mar 17, 2015 6:35 PM GMT
    A. Just don't watch it.
  • Posted by a hidden member.
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    Mar 17, 2015 6:41 PM GMT
    C.

    You just need to incease the temperature of water to 100 degree celcius. I think the heat from the below is the only source which is contributing in increasing the temperature of water.
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    Mar 17, 2015 7:14 PM GMT
    __morphic__ saidYou just need to incease the temperature of water to 100 degree celcius...
    that is exactly the story.
    A or C are good choices
    So faster with the lid on because incrementally less heat loss.

    additionally:
    water boils at 100C, freezes at 0C. going below 0c will not make it freeze faster or harder. same with the boiling water going above 100c. the behavior of water really defines the earth.
  • Destinharbor

    Posts: 4433

    Mar 17, 2015 8:02 PM GMT
    A is the answer. As the water at the top of the pot rises above the ambient air temp, heat will escape. If you put a lid on it, the escaping heat will continue to heat the air but the temp of the trapped air will rise reducing the loss. Thus more is held in the water causing it to boil faster.
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    Mar 17, 2015 8:09 PM GMT
    Destinharbor saidA is the answer. As the water at the top of the pot rises above the ambient air temp, heat will escape. If you put a lid on it, the escaping heat will continue to heat the air but the temp of the trapped air will rise reducing the loss. Thus more is held in the water causing it to boil faster.

    yeah, this makes sense.
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    Mar 17, 2015 8:10 PM GMT
    Yes, but assuming that the burner is turned on high, heat loss from above is small compared with heat flowing in, so you would never measure this effect. You might see it if you were trying to heat the water with some heat source that was barely 100C.

    BTW, with the lid in place, air becomes displaced by steam, which is less oxidizing. Obviously the lid also promotes condensation and recycling of the steam, so that you don't loose water to the atmosphere as fast.


    icon_confused.gif So... slow news day...
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    Mar 17, 2015 9:13 PM GMT
    Trick question: what about the air pressure under the lid if you're using one? Does that affect the timing? (I don't know the answer but I thought I'd throw that potential monkey wrench in there.)
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    Mar 17, 2015 10:42 PM GMT
    Unless you're using a pressure cooker, there is unlikely to be a measurable increase in pressure until you're already at a rolling boil. Even then, it's only slight.

    If you're that bored, get out a couple of identical pots and some stop watches.
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    Mar 18, 2015 12:27 AM GMT
    My brain hurts thinking about this. icon_confused.gificon_eek.gif
  • Posted by a hidden member.
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    Mar 18, 2015 12:29 AM GMT
    The lid on helps it boil faster icon_smile.gif
  • monet

    Posts: 1093

    Mar 18, 2015 1:13 AM GMT
    Water will definitely come to a boil faster if you put a lid on the pot.

    If you don't believe me just go do a little science experiment in your kitchen.

    Note: Use two pots each able to hold at least a quart or two of water and the difference will be very obvious.
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    Mar 18, 2015 5:09 AM GMT
    Let's focus on what's important here...

    Why are we boiling the water?
    Steaming artichoke hearts?
    Sanitizing anal toys?
    What's our motivation here?
  • AMoonHawk

    Posts: 11406

    Mar 18, 2015 5:46 AM GMT
    Faster if you heat up the pot, microwave the water then put it in the pot when it is hot ... Otherwise A
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    Mar 18, 2015 7:18 AM GMT
    mindgarden saidLet's focus on what's important here...

    Why are we boiling the water?
    Steaming artichoke hearts?
    Sanitizing anal toys?
    What's our motivation here?

    What, you want me to let the cat out of the bag?
  • jeep334

    Posts: 408

    Mar 18, 2015 7:43 AM GMT
    monet saidWater will definitely come to a boil faster if you put a lid on the pot.

    If you don't believe me just go do a little science experiment in your kitchen.

    Note: Use two pots each able to hold at least a quart or two of water and the difference will be very obvious.

    I like the experiment idea but how do you when a covered pot of water is boiling unless tie lid is glass. Even then with the amount of steam involved it will be difficult to tell the actual time of boiling. I always cover the pot because I just think it boils faster that way. Watching the experiment would seem to be tiresome because it really does seem that a watched never boils, which is why I assume bon_pan never watches it. Maybe he's doing more constructive things in the interim. icon_cool.gif
  • buddycat

    Posts: 1874

    Mar 18, 2015 8:59 AM GMT
    I think equally but the water evaporates but doesn't escape with a lid on it as much.
  • monet

    Posts: 1093

    Mar 18, 2015 3:18 PM GMT
  • Olympus1991

    Posts: 46

    Mar 18, 2015 6:17 PM GMT
    Add a pinch of salt to the water ;)
  • FRE0

    Posts: 4863

    Mar 18, 2015 6:57 PM GMT
    A. It will definitely boil faster with the lid on, but assuming that the burner puts out plenty of heat, the difference will be small. Unless you actually accurately time it, you will not notice the difference. Also, determining the exact instant at which boiling begins will not be easy so probably you could not accurately make the comparison anyway. If you try it, be sure to measure accurately the amount of water you use and be sure that the starting temperature is the same.

    To be really scientific, you will need to repeat the experiment several times and tabulate the results.
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    Mar 18, 2015 10:08 PM GMT
    FRE0 saidA. It will definitely boil faster with the lid on, but assuming that the burner puts out plenty of heat, the difference will be small. Unless you actually accurately time it, you will not notice the difference. Also, determining the exact instant at which boiling begins will not be easy so probably you could not accurately make the comparison anyway. If you try it, be sure to measure accurately the amount of water you use and be sure that the starting temperature is the same.
    To be really scientific, you will need to repeat the experiment several times and tabulate the results.

    Since water boils at different temperatures depending on your altitude I was thinking that you could bring a pot of water to boil and measure its temperature with a digital thermometer and use only the temperature as the point where you consider it boiling.

    In a laboratory setting you could have a digital timer connected to the on/off switch to your heat source so that the timer starts when the heat is applied, and the digital thermometer is connected to the timer, or everything is connected to a computer which is logging the collected data (every millisecond, for example). In that setting you would certainly see that with the lid it boils sooner. Maybe only a few hundred milliseconds sooner, maybe even a few thousand.

    In a kitchen setting it's very likely irrelevant since you're probably busy cutting and chopping or doing something and won't notice when the water starts boiling. And if you always use a lid I doubt if you'll see any reduction in your gas/electric bill.

    It was a slightly rhetorical question, originally asked by a roommate's girlfriend many years ago. He and his girlfriend were physics majors. At the time I remember thinking it was a silly question and that the lid wouldn't make any difference but I later realized that it would make some difference but it'd be too small to matter in practice.

    I started thinking about it again when I got an induction stove; with the induction stove it's really irrelevant since the water comes to boil so quickly that I'm still amazed.

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    Mar 18, 2015 10:20 PM GMT
    Olympus1991 saidAdd a pinch of salt to the water ;)

    A lot more as it turns out. Pasta is made without salt and it'll help whatever your making if you make the water taste salty, but not too salty. For example, when I'm cooking spaghetti I use an 8 quart pot and put at least 6 quarts of water in it and I use a tablespoon of salt. I also pour a tablespoon or so of oil in it (eyeball measurement); it helps keep it from foaming up too much.
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    Mar 19, 2015 5:55 AM GMT
    Well, actually, I boil water in the lab every. fucking. day. Usually in pyrex flasks, so it's easy to see when boiling starts. If you don't stop it at the exact right moment, half of the stuff usually foams over onto the lab bench like a Jerry Lewis lab accident, and starts charring. So yes, you have to sit there and watch water boiling (and surf RealJock on your phone) We add boiling chips to make it boil faster (look it up), unless there is a magnetic stir bar going (which slows down the boiling anyway) and funnel-shaped lids to help recycle the condensate. (Haven't bought those in 20 years and can't recall the exact esoteric name - basically I have a lifetime supply already.) Of course, if maintaining the precise volume were important, one would add a condenser to the top. Oh, and half the time, I'm doing it under a stream of nitrogen or mixed gas (to exclude oxygen) so that screws up everything.

    If you really want to have fun with it, I've also got a rotary evaporator. I don't usually use it for water, but you could. It can also turn a bottle of cheap wine into a small glass of nasty schnapps. If anyone were that bored. icon_wink.gif

    It's this one:

    8010000.jpg
  • Posted by a hidden member.
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    Mar 19, 2015 7:11 AM GMT
    Whatever you do, don't try to boil water with a microwave.
    https://youtu.be/1_OXM4mr_i0
  • Posted by a hidden member.
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    Mar 19, 2015 3:15 PM GMT
    first post where "Obama" hasnt been mentioned

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