Articles, Blog

Does Hot Water Freeze Faster Than Cold Water?

November 10, 2019


Intro 🎵 Here’s a scientific mystery for you: Does
hot water freeze faster than cold water? The answer is: We don’t know. You’re probably thinking, how can we not
know? I mean, we’ve all got water. Most of us have a freezer. This seems like a pretty simple experiment. Well you’re right, it is. It also isn’t. The experiment has been performed by brilliant people all over the world. And in those experiments, sometimes hot water freezes faster than cold water. And sometimes it doesn’t. And either way, the results of the experiment are not reproducible. The observation that hot water will freeze
faster than cold water is called the Mpemba Effect. It’s named after Erasto Mpemba, who noticed the effect in 1963 when he was just thirteen years old and making ice cream with his classmates. He noticed that the ice cream mixture made with hot milk froze faster than the mixture made with cold milk. However, he wasn’t the first person to make this claim. Aristotle said the same thing in the year 4 BCE. Just, you know, not about ice cream. René Descartes and Francis Bacon also believed that hot water froze faster than cold water. But scientists aren’t convinced that the
Mpemba Effect is actually a thing. Here’s the problem. When you have any two samples of water that’s just ordinary tap water, one of them will always freeze first. That’s because the mixture of impurities in the water will be slightly different. The differences in the composition, size, and position of those impurities can make the freezing point of water vary by several degrees. Hot tap water will freeze before cold distilled water if you control for all other conditions because the impurities in the tap water mean that it just freezes at a higher temperature. So in that case, the hot water does freeze first, but not because it’s hot. If the Mpemba Effect is a thing, and warmer water really does freeze faster, there are a lot of theories for why that might happen. Evaporation is the simplest and probably the best one. Some of the hot water will evaporate as it cools, meaning there’s just less water to freeze, so it doesn’t take as much time. But the Mpemba Effect has been observed while using sealed containers, which prevented evaporated water from escaping. Other researchers who have looked into the Mpemba Effect claim is has to do with convection currents, the way the water moves around as it heats. Or covalent bonds. Or how hot water holds less dissolved gas, which maybe does… something. They’re not really sure. Want to test it yourself? Stick some water
in your freezer and see if you notice something weird. Who knows, maybe you’ll get an effect named after you. Thanks for asking, and thanks to all of our
patrons on Patreon who keep these answers coming. If you’d like to submit questions to be answered, or get these Quick Questions a few days before everyone else, go to patreon.com/scishow. And don’t forget to go to youtube.com/scishow and subscribe! Outro 🎵

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100 Comments

  • Reply Vae Victis July 8, 2016 at 7:47 am

    who knows maybe you'll get an effect named after u lol

  • Reply Viet Nguyen July 11, 2016 at 11:40 pm

    No matter what video I watch, what research I study, what book or forums I read, no one talks about the exact temperature of the waters they used. It's always "hot" water but never how hot, nor hold cold.

  • Reply Michael Furtado July 12, 2016 at 6:34 pm

    Logically speaking wouldn't hot water HAVE to freeze slower than cold water. If you're freezing hot water, it will eventually become cold water but by now, time would have past and the originally cold water would be more frozen than the hot water would be. Continue this pattern and the cold water will have to be more frozen than hot water.

    Correct me if I'm wrong because I'm genuinely curious.

  • Reply eventhorizon July 14, 2016 at 4:21 am

    I did it with tap water- the cold froze first for me- different times, different water sources (well, city)…

  • Reply Julian Valdez July 19, 2016 at 3:17 pm

    Aristotle was in the 4th century bce and not the year 4 bce

  • Reply blipzero August 7, 2016 at 3:43 am

    the reason is the atmospheric pressure of where you on top of the mountain or down at sea level duh ask any one from alaska duh

  • Reply blipzero August 7, 2016 at 3:44 am

    not only that but at what temp will the water be hot at will also differ.

  • Reply ananixon August 12, 2016 at 10:41 pm

    Do you know in which text Aristotle talked about this? It'd be good to check it out…

  • Reply tpsu129 August 14, 2016 at 2:17 pm

    It's BC and not BCE.

  • Reply Josh Greening August 15, 2016 at 4:48 pm

    should do a video on hot and cold water which one boils first and why.
    I mean I already know, but it would make for a cool video lol

  • Reply KeenTam August 16, 2016 at 3:26 pm

    i dont undrstnd yur explntion

  • Reply Kenny Phillips August 17, 2016 at 7:26 pm

    I did this with two freezer bags, the same mass of distilled water from the same source (the more the merrier, a kilogram would be ideal), and the bags being sealed with the water at the same temperature, with the air sucked out. So I eliminated most contaminants, loss of mass from evaporation, loss of energy through latent heat of evaporation, and any large difference in dissolved gasses. Cooled one bag to just a few degrees above freezing in ice water, put other bag in boiling water, dried both bags, tossed them in freezer on top of sheet of styrofoam (to eliminate conduction.) Easy to try … everyone should do it. Several times.

  • Reply Dimitra Kambouris De Hoog September 3, 2016 at 1:13 am

    what about the energy of activation? Phase changes?

  • Reply Andrew Brookes September 4, 2016 at 5:05 am

    Could we not use two precise measurments of distilled water (one heated and one not )in two seperate freeezers with equal conditions on a timer? How would that not produce accurate enough results?

  • Reply Henry Mei September 5, 2016 at 1:44 am

    Aside from the absolute time it takes, what about the rate of temperature change? Larger gradient would indicate a larger rate, correct?

  • Reply Turbo September 6, 2016 at 3:45 am

    what would be cooler in 5 hours when placed on a bed?
    a blanket sitting at room temp or a blanket right out of the dryer?

  • Reply Debankur Jana September 11, 2016 at 5:12 am

    i've always heard that…and i never really understood why or how it was. Good to finally know i wasn't the only one.

  • Reply Mohammed Moumene September 12, 2016 at 12:32 pm

    a piece of your hair froze!

  • Reply Nigel October 3, 2016 at 1:41 pm

    Why not just use two samples of distilled water, to remove the particles variable.

  • Reply akuapiatas October 15, 2016 at 9:19 pm

    hot water freezes faster because it has expanded thus no need for it to expand whilst freezing

  • Reply PCreeper394 October 19, 2016 at 4:04 pm

    Am I the only one who doesn't understand the problem here? If there aren't any impurities, water freezes at 0ºC at atmospheric pressure. So, ALL the water freezes at that temperature, regardless of its initial temperature, but hot water takes longer to reach the freezing point. Therefore cold water should freeze first, shouldn't it?

  • Reply Raffaella Di Nuzzo October 22, 2016 at 3:27 am

    How do lizards regrow their tale

  • Reply GTIP productions October 25, 2016 at 11:49 am

    ok I have an Idea freeze two identically pure glasses with 500 ml of water in each and wait

  • Reply JosiahTV November 7, 2016 at 8:36 pm

    This Man Is Smart bc we wont tell it apart bc u put hot and cold water and cant tell which is which

  • Reply Aaron Klapheck November 18, 2016 at 9:27 pm

    Freezing point of liquids. Completely pure water with no nucleation sites can be brought down close to absolute zero without freezing. Completely pure water is physically (and maybe theoretically) impossible as there is no way to eliminate every single atom in a container except for hydrogen and oxygen atoms bound in water. The container itself has atomic imperfections which will function as nucleation sites once the water is cold enough (-10 C or so depending on a lot of factors). However, if you were to use a theoretically-perfect surface free of imperfections (such as a pure carbon container where all carbon atoms are bonded to other carbon atoms) and use this to hold the theoretically-perfectly pure water then you could get the water very close to absolute zero before it would freeze. However, once the water and container are close to absolute zero quantum weirdness gets involved and everything we thought we knew about physics goes out the window. Because we don't live in a theoretically perfect world with perfect pure water or perfect containers freezing has more to do with the level of impurities and imperfections than the average molecular motion of molecules (temperature).

  • Reply Jaren Cascino November 20, 2016 at 3:27 pm

    wouldnt the one that is closer to the freezing point freeze quicker…. Like hot water turns cold before it freezes completely.

  • Reply Quirky Kirk November 23, 2016 at 10:02 pm

    Get a skilled physicist to mathematically solve it. 😐

  • Reply Doãn Vi January 2, 2017 at 4:52 pm

    the more close and simple it is, the more it get complicated lol

  • Reply Peter Diamore January 9, 2017 at 4:26 am

    I got to guess 🙂 boiling water is drier then colder water

  • Reply Joshua Montgomery January 18, 2017 at 5:43 pm

    Could it be that when water is settling from a higher temperature it can settle in a more ordered fashion. Since hot water has heat energy the molecules can vibrate into the positions that would best support nucleation. Cold water may not have the energy to find optimal molecular structure for freezing and optimization of hydrogen bonding.

  • Reply DarkKrusty February 1, 2017 at 4:30 pm

    it is interesting because few years ago when the UK had really cold weather it was even colder in syberia (colder than it has been for awhile) it was so could if you tossed boiling water up into the air it froze in the air, which is interesting because if its that cold to do that with boiling why do you not freeze in an instant?

  • Reply Dr Zombiecakes February 7, 2017 at 3:08 am

    I did this for my science fair project in 6th grade which is an idea I thought of all by myself and completed all by my self. The hot water froze first.

    My teacher told me it was dumb, that I was too, and failed me.

  • Reply AirlessMICRO February 8, 2017 at 5:37 pm

    Does anyone else have hot water pipes that freeze in their house during cold nights but the cold water pipes don't freeze? I'm really confused about this.

  • Reply spacewater7 February 9, 2017 at 6:12 am

    Total misinformation. Even in a sealed container evaporation cools the water and heats the lid. Eliminating all gasses from the vial is the only way.

  • Reply Shahzaib Khan February 18, 2017 at 7:06 pm

    +Vsauce made a video on those Brachistochrone/Tautochrone things, maybe
    that's what's happening to the hot water/cold water freezing rate as
    well? please tell me if I'm wrong or right

  • Reply Collin Gentry February 19, 2017 at 11:30 pm

    The real question is which came first, the hot water or the cold water?

  • Reply Tom Scott March 13, 2017 at 12:12 pm

    Aristotle was long dead in 4 BC.

  • Reply Louis Melahn March 20, 2017 at 8:05 pm

    There is no way that Aristotle made this claim in 4 B.C., since he died in 322 B.C. (Probably a typo in there somewhere.)

  • Reply Victoria Akanno April 13, 2017 at 11:54 pm

    This was my 2nd grade science fair project 😂

  • Reply Batabii May 21, 2017 at 11:24 am

    hold on couldn't they just do the test with all the water impurities removed

  • Reply Campbell DIT May 23, 2017 at 3:05 am

    anyone else think this was about quantum physics 0:24

  • Reply Apurupa Margapuri May 23, 2017 at 8:25 am

    When i first heard about this I thought maybe it was because the rate of heat transfer for the hot water is faster? According to Newton's law of cooling, the rate of heat transfer is proportional to the temperature difference between the two bodies and since the hot water and freezer have a higher temperature difference, the heat should be transferred out of the water quicker. but then again there must be a point where the the hot water and cold water reach the same temperature. Idk, i dont think I have it totally right. Can someone point out the error I'm making? D:

  • Reply Numeky May 26, 2017 at 3:45 am

    maybe try doing a vid of it vs just flaping your face.

  • Reply TheEndersDragon May 26, 2017 at 6:36 am

    Mpemba was the ultimate hipster. He froze his ice cream before it was cool.

  • Reply Goran Micevski May 26, 2017 at 12:03 pm

    i can make hot water to freeze faster then cold water, in 100% of cases , and it is not mpemba effect :)))

  • Reply James Fredrick June 4, 2017 at 3:41 pm

    does the amount of potential energy have a variant in the freezing of water

  • Reply Diego Crescente June 26, 2017 at 3:17 am

    There's a Newton Law that predicts that the rate at which something cools down depends exponentially on th difference of temperature between THAT something and the environment, so this could be a plausible explanation. I have tried this in the laboratory with some hot crisols and it really worked: crisols who were in the oven at 400°C cooled faster than those at 150°C

  • Reply pvildep July 11, 2017 at 8:17 pm

    How could you put this video up without testing the theory out yourself????? All you need is two samples of water, one hot and one cold, of the same consistency. So, um let's think about this…..oh yeah. DISTILLED WATER. Pure water. Water that has been rendered free of any impurities. Heat one. Don't heat the other. Stick both in the freezer. Do the experiment three times for redundancy. Done.

  • Reply Canada The Countryball August 16, 2017 at 11:57 pm

    I did this for my science fair project

    I got a B

  • Reply Micha Grill August 28, 2017 at 6:49 pm

    Could we do the experiment with destilled water? 🙂

  • Reply Foton September 18, 2017 at 2:52 am

    Use distilled water

  • Reply Arbiter and Chara Dreemurr September 19, 2017 at 7:47 pm

    Is it more often faster or less often.

  • Reply Jeff Stewart October 12, 2017 at 7:36 pm

    My grandfather told me this back in the 1970's. He said his first car didn't have any anti-freeze, so he used to drain the water when it was cold, and refill it when he needed to go somewhere. He also said that if you put the hot water back in the engine, it would freeze faster than putting cold water in. This made no sense to me, and I was probably 9 or 10 years old when he shared this with me. Being a scientific type, I did not believe him. My grandmother and I spent a day just heating and freezing samples of tap water to test his claim. Our results were inconclusive. Completely random results. Sometimes the boiling water would freeze a minute before the 40 degree F water. Sometimes the cold water would freeze first. I learned a lot about variables and rigor from my grandmother that day, but I also learned that my grandfather wasn't necessarily full of crap.

  • Reply Valerie Pallaoro November 11, 2017 at 4:58 pm

    Those patreon guys need to up their game "who keep these answers coming' .. there was no (and in so many glorious ways that I'm rushing to empty the freezer and to the experiment myself) answer to this question. Keep up the good, excellent, work!!

  • Reply chu Harry November 24, 2017 at 5:14 am

    Sodium fluoride wich is more plentiful in boils water
    gives condensation nucleus

  • Reply Existenceisillusion November 24, 2017 at 8:04 am

    There's a lot of hate on this topic. Veritasium gives a more complete and detailed "We don't know" answer.

  • Reply dwd ded December 3, 2017 at 2:43 am

    How did Aristotle freeze water?

    Hello sci show answer me , he didn't have a freezer soooooo wtf ? 😇

  • Reply Guilherme Fernandes Dias Canalli December 11, 2017 at 1:32 am

    Maybe when the water is hot boiling it is losing energy faster by boiling and then freeze fast

  • Reply UY KI VINES December 14, 2017 at 8:49 am

    Robot

  • Reply Pietro Tettamanti December 17, 2017 at 4:39 pm

    The answer is simple, and it has nothing to do with the water being cold or not. Water can supercool in some cases, and the conditions for supercooling are so delicate that two water containers in the same freezer can freeze differently. Surely hot water is unfavoured because no matter what you do, you'll have to remove that excess energy first (which takes time), while you haven't to with cold water. But cold water can supercool and start freezing after hot water has been cooled to 0°C (and started freezing). It also doesn't happen sometimes, and as I said the conditions are really delicate, so it makes sense that the experiment gives different results every time.

  • Reply Kendrick Hong January 7, 2018 at 3:47 pm

    "freezes at a higher temperature"???

  • Reply Dakila Lozano January 7, 2018 at 10:50 pm

    my mother tells us to let the food cool first before putting it in the ref 😅😁

  • Reply Robert 'Skip' Berne January 9, 2018 at 2:14 pm

    Not one of you so called scientists ever asked the question "does that same ice melt faster?" the answer is yes. it is not the same structure as the other. you all are stupid.

  • Reply Misael De León January 10, 2018 at 10:57 pm

    My top water freeze faster than cold or hot water

  • Reply Harshit Yashwardhan February 2, 2018 at 3:36 pm

    Iam going to that experiment.

  • Reply NO MA'AM February 10, 2018 at 9:58 pm

    So cant they test with ultra purified water? The kind used with processor chips.

  • Reply Mengele4 February 11, 2018 at 7:16 am

    Could it be for the faster movement of the molecules when it's hot, or maybe random bubbles that might help the crystallization of the water?. Can those option be viable? o.O

  • Reply Sean Not-telling February 11, 2018 at 7:30 am

    I used to work at an ice arena and when we used hot water during the resurface process is always seemed to freeze much faster then the cold and also gave a higher gloss to the surface. The gloss was more likely do to melting the surface ans smoothings things out a little better.

  • Reply Klemeninio Browni February 11, 2018 at 2:58 pm

    You only made this video because a black kid did something

  • Reply Subham Biswas February 14, 2018 at 1:12 pm

    Maybe the reason lies in entropy of the system

  • Reply Flopdoodle February 17, 2018 at 11:13 pm

    Prosition: hot water is less dense so there's less water to freeze, therefore it freezes faster

  • Reply Elizabeth Shaw February 19, 2018 at 9:53 pm

    I was born in 1963! I have found warm water to freeze faster than cold when I'm making ice cubes.

  • Reply princetlance February 20, 2018 at 5:04 am

    I mean this with no disrespect, but shut ur damn mouth. This is legit, whether u think so or not. In winter wash my car with warm water and everything freezes over the next day, and I mean like super freeze. My windshield wipers don’t even move because of how hard the ice is. So I switched to cold water and no time since my vehicle froze. And don’t tell me about temperature difference. I’ve done it too many times for it to not be conclusive. And when I say wipers don’t move I don’t mean on the surface, I mean down in the wiper motor the gears were frozen solid. I actually had to spray hot water on it to get it moving again then used the blow gun to dry the water so it wouldn’t freeze again

  • Reply Floyd Wheatley February 25, 2018 at 12:41 am

    I did this for my science fair project and the hot water with dirt froze at the same time but the hot water without dirt froze last

  • Reply sundu21 March 25, 2018 at 8:07 pm

    What about Newton’s law of cooling where rate of cooling is directly proportional to the temp difference ?

  • Reply Alex Joseck April 11, 2018 at 12:56 am

    It is called the MPEMBA EFFECT…… The TANZANIAN…. Proud Tanzanian give him credit don't go too far

  • Reply Dicky Dharma April 26, 2018 at 7:04 pm

    this is the first time I see scishow answers "we dont know" lol

  • Reply Germán M. May 2, 2018 at 11:54 am

    your hair makes you look like a douche bag

  • Reply Reginald Finley May 5, 2018 at 4:06 pm

    The crystals are also larger and less cloudy. I did this experiment a decade ago.

  • Reply Phantom Raven June 6, 2018 at 1:12 am

    Use room temperature water for freezing problem solved

  • Reply Daryl Nolan July 26, 2018 at 11:10 pm

    could it be that the container is usually the first to drop to below freezing and that the hot water molecules are more active in there movement hit the cold container and set off a chain reaction

  • Reply Rhett A August 20, 2018 at 7:38 pm

    Correction…adding impurities (i.e. non-volatile solutes) to water DECREASES the freezing point of the water "solution"; the concept is known as 'freezing point depression'

  • Reply I'm not Wanda August 27, 2018 at 7:59 pm

    They can't cure the common cold either; its complicated

  • Reply Lee Brewer September 1, 2018 at 11:03 pm

    BCE = Before Church Era – or BC (Before Christ)
    .

  • Reply 383 chevy October 7, 2018 at 8:02 am

    Yes.

  • Reply 383 chevy October 7, 2018 at 8:02 am

    Adding salt to iced water makes it colder. Thank me later😁😆

  • Reply flop flop6 October 18, 2018 at 12:31 pm

    Now the question is does cold water boil faster than hot water?

  • Reply vGullible - October 30, 2018 at 2:41 am

    I have a question- is water always wet?

  • Reply Cap'n SuperFan January 17, 2019 at 8:12 pm

    0:49 Wait… If Erasto Mpemba discovered the Mpemba Effect (his namesake) with milk…
    Then why the actual heck haven't we been trying this out with milk instead of water????

  • Reply kid kurmudgeon January 29, 2019 at 3:16 pm

    This was our 1st home work experiment in my science and pseudoscience class in college. I Its too bad most people cant tell 1 from the other.

  • Reply Console February 3, 2019 at 11:33 am

    Wasn't sure of what he said. Requires more subtitles.

  • Reply Leo Fath February 6, 2019 at 10:19 pm

    You cant perform the experiment in a freezer.

  • Reply Paul February 13, 2019 at 5:31 pm

    I'm guessing no.

  • Reply Alex Maxwell February 25, 2019 at 9:04 am

    Freeze a glass of water then when it thaws heat it up and see if it freezes first

  • Reply Brittbratthekittycat March 13, 2019 at 6:01 pm

    He kind of sounds like Daily Dose of Internet.

  • Reply Turkey Bowlwinkle April 17, 2019 at 5:14 am

    Frozen water freezes first.

  • Reply Caleb Johnsen April 25, 2019 at 5:02 am

    Water does not freeze on it's own. Ice crystals require a nucleation point to form around. Tests should control for how different impurities are introduced into the water while varying how much boiling is taking place.
    I assume that how the impurities are distributed is the cause of the cascading effect.

  • Reply Thomas Conrow June 24, 2019 at 2:04 am

    A given volume of hot water is less dense than the same volume of cold water. Might that have something to do with it?

  • Reply k4ot1c July 26, 2019 at 9:08 pm

    that was a long way to say "IDK"

  • Reply Solad August 26, 2019 at 3:33 pm

    I'm just commenting so that there will be 1,000 comments.

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