WEBVTT - How Can Hot Water Freeze Faster Than Cold Water?

0:00:02.040 --> 0:00:09.520
<v Speaker 1>Welcome to brain stuff from How Stuff Works. Hey, I'm

0:00:09.600 --> 0:00:12.840
<v Speaker 1>Christian Saga and this is brain stuff pop quiz. I'm

0:00:12.880 --> 0:00:15.280
<v Speaker 1>thinking of a substance. Let's see if you can guess

0:00:15.360 --> 0:00:19.040
<v Speaker 1>what it is. And it's pure form. It's odorless, tasteless,

0:00:19.120 --> 0:00:22.720
<v Speaker 1>and nearly colorless. It's in your food. In fact, a

0:00:22.840 --> 0:00:25.360
<v Speaker 1>lot of the stuff you use every day either contains

0:00:25.400 --> 0:00:29.160
<v Speaker 1>it or was manufactured using it. It's even in your body.

0:00:29.240 --> 0:00:31.639
<v Speaker 1>Can you guess what it is? If you guessed water,

0:00:31.800 --> 0:00:34.320
<v Speaker 1>then you're correct. Water is one of the most important

0:00:34.320 --> 0:00:37.240
<v Speaker 1>substances on earth as far as life goes, at least,

0:00:37.479 --> 0:00:40.519
<v Speaker 1>and it can do some weird stuff. For example, it

0:00:40.600 --> 0:00:44.440
<v Speaker 1>reaches a maximum density at around four degrees celsius and

0:00:44.440 --> 0:00:48.440
<v Speaker 1>then becomes less dense before it freezes. And here's another

0:00:48.479 --> 0:00:52.320
<v Speaker 1>strange thing. Hot water can freeze faster than cold water.

0:00:52.600 --> 0:00:56.400
<v Speaker 1>But why, Okay, this is a very old question. In fact,

0:00:56.440 --> 0:01:00.200
<v Speaker 1>Renee Descartes thought about it, and Francis Bacon before him,

0:01:00.320 --> 0:01:04.360
<v Speaker 1>Aristotle pondered the mystery too. Today we call this phenomenon

0:01:04.480 --> 0:01:08.880
<v Speaker 1>the Impemba effect, after a guy named Erasto Impemba, who

0:01:08.920 --> 0:01:11.440
<v Speaker 1>first observed the effect on ice cream when he was

0:01:11.520 --> 0:01:15.040
<v Speaker 1>just thirteen years old. His teacher, for the record, laughed

0:01:15.040 --> 0:01:18.800
<v Speaker 1>at him, Well who's laughing now? Turns out Rasto was

0:01:18.840 --> 0:01:21.679
<v Speaker 1>onto something big, and teams of experts would spend the

0:01:21.720 --> 0:01:25.160
<v Speaker 1>next few decades trying to explain why water behaves this way.

0:01:25.560 --> 0:01:28.800
<v Speaker 1>Scientists around the world cooked up dozens of theories, and

0:01:28.880 --> 0:01:32.160
<v Speaker 1>none were able to completely explain the process. But as

0:01:33.360 --> 0:01:36.800
<v Speaker 1>that may have changed. A research assistant at the University

0:01:36.800 --> 0:01:40.559
<v Speaker 1>of Zagreb in Croatia claims that convection currents in warm

0:01:40.600 --> 0:01:43.919
<v Speaker 1>water cause it to cool more rapidly, and the Royal

0:01:43.959 --> 0:01:47.240
<v Speaker 1>Society of Chemistry agrees with him. They actually gave the

0:01:47.240 --> 0:01:50.920
<v Speaker 1>guy a thousand pound prize for his experiments. But he's

0:01:50.960 --> 0:01:54.160
<v Speaker 1>not the only contender for a solution. A team of

0:01:54.200 --> 0:01:58.640
<v Speaker 1>physicists at the Non Young Technological University in Singapore took

0:01:58.680 --> 0:02:02.080
<v Speaker 1>the question to a much smaller level. They claim that

0:02:02.120 --> 0:02:05.080
<v Speaker 1>the answer lies in the bonding. Not you know, hanging

0:02:05.080 --> 0:02:09.560
<v Speaker 1>out with friends type bonding, but molecular bonding two kinds actually.

0:02:10.040 --> 0:02:13.200
<v Speaker 1>You see, every water molecule is made of two hydrogen

0:02:13.240 --> 0:02:17.000
<v Speaker 1>atoms bonded to a single atom of oxygen. These are

0:02:17.040 --> 0:02:21.200
<v Speaker 1>covalent bonds, which means that they share electrons between one another.

0:02:21.639 --> 0:02:25.120
<v Speaker 1>This is a chemical bond. Separate water molecules are bound

0:02:25.120 --> 0:02:28.200
<v Speaker 1>to their neighbors by weaker hydrogen bonds, which occur when

0:02:28.200 --> 0:02:31.480
<v Speaker 1>a hydrogen atom from one water molecule is close to

0:02:31.480 --> 0:02:35.480
<v Speaker 1>the oxygen atom of another water molecule. This is an

0:02:35.480 --> 0:02:39.320
<v Speaker 1>electromagnetic attraction and it's what gives water some of its

0:02:39.320 --> 0:02:43.160
<v Speaker 1>strange abilities, like it's unusually high boiling point of one

0:02:43.240 --> 0:02:47.120
<v Speaker 1>hundred degrees celsius that's two hundred and twelve degrees fahrenheit.

0:02:47.720 --> 0:02:51.040
<v Speaker 1>So these scientists in Singapore argue that the Impemba effect

0:02:51.120 --> 0:02:54.280
<v Speaker 1>comes from an interaction between the covalent bonds, you know,

0:02:54.360 --> 0:02:58.400
<v Speaker 1>the inner water molecule bonds, and the hydrogen bonds between

0:02:58.520 --> 0:03:02.680
<v Speaker 1>different molecules. Here's how they think it works. When water

0:03:02.760 --> 0:03:07.000
<v Speaker 1>molecules are close together, their natural repulsion causes the covalent

0:03:07.040 --> 0:03:10.920
<v Speaker 1>bonds to stretch and store energy. As the water warms up,

0:03:11.160 --> 0:03:14.960
<v Speaker 1>it becomes less dense, the hydrogen bonds stretch as the

0:03:15.000 --> 0:03:19.320
<v Speaker 1>molecules move further apart. When these hydrogen bonds stretch, they

0:03:19.360 --> 0:03:22.760
<v Speaker 1>allow the covalent bonds to shrink and release their energy.

0:03:23.160 --> 0:03:26.480
<v Speaker 1>This is equivalent to cooling. So according to the non

0:03:26.560 --> 0:03:30.680
<v Speaker 1>Young theory, hot water is essentially able to release energy faster,

0:03:31.120 --> 0:03:33.880
<v Speaker 1>leading to a quicker freeze. It's important to note that

0:03:33.919 --> 0:03:36.920
<v Speaker 1>at this point that work hasn't been peer reviewed, so

0:03:36.960 --> 0:03:39.560
<v Speaker 1>it's not a sure thing yet, but even if it's

0:03:39.600 --> 0:03:42.600
<v Speaker 1>just a contributing factor, it's a promising lead to a

0:03:42.680 --> 0:03:51.360
<v Speaker 1>question that's puzzled humanity for some twenty hundred years. Check

0:03:51.360 --> 0:03:53.440
<v Speaker 1>out the brain stuff channel on YouTube, and for more

0:03:53.480 --> 0:03:56.000
<v Speaker 1>on this and thousands of other topics, visit how stuff

0:03:56.000 --> 0:04:10.520
<v Speaker 1>works dot com.