May 16, 2016 • 4 mins
At first, it sounds crazy -- wouldn't hot water take longer to freeze? Weirdly enough, the opposite is sometimes true. Join Christian to learn more about a mystery that's puzzled humanity for centuries in this episode of BrainStuff.
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Episode Transcript
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Speaker 1 (00:02):
Welcome to brain stuff from How Stuff Works. Hey, I'm
Christian Saga and this is brain stuff pop quiz. I'm
thinking of a substance. Let's see if you can guess
what it is. And it's pure form. It's odorless, tasteless,
and nearly colorless. It's in your food. In fact, a
(00:22):
lot of the stuff you use every day either contains
it or was manufactured using it. It's even in your body.
Can you guess what it is? If you guessed water,
then you're correct. Water is one of the most important
substances on earth as far as life goes, at least,
and it can do some weird stuff. For example, it
reaches a maximum density at around four degrees celsius and
(00:44):
then becomes less dense before it freezes. And here's another
strange thing. Hot water can freeze faster than cold water.
But why, Okay, this is a very old question. In fact,
Renee Descartes thought about it, and Francis Bacon before him,
Aristotle pondered the mystery too. Today we call this phenomenon
(01:04):
the Impemba effect, after a guy named Erasto Impemba, who
first observed the effect on ice cream when he was
just thirteen years old. His teacher, for the record, laughed
at him, Well who's laughing now? Turns out Rasto was
onto something big, and teams of experts would spend the
next few decades trying to explain why water behaves this way.
(01:25):
Scientists around the world cooked up dozens of theories, and
none were able to completely explain the process. But as
that may have changed. A research assistant at the University
of Zagreb in Croatia claims that convection currents in warm
water cause it to cool more rapidly, and the Royal
Society of Chemistry agrees with him. They actually gave the
(01:47):
guy a thousand pound prize for his experiments. But he's
not the only contender for a solution. A team of
physicists at the Non Young Technological University in Singapore took
the question to a much smaller level. They claim that
the answer lies in the bonding. Not you know, hanging
out with friends type bonding, but molecular bonding two kinds actually.
(02:10):
You see, every water molecule is made of two hydrogen
atoms bonded to a single atom of oxygen. These are
covalent bonds, which means that they share electrons between one another.
This is a chemical bond. Separate water molecules are bound
to their neighbors by weaker hydrogen bonds, which occur when
a hydrogen atom from one water molecule is close to
(02:31):
the oxygen atom of another water molecule. This is an
electromagnetic attraction and it's what gives water some of its
strange abilities, like it's unusually high boiling point of one
hundred degrees celsius that's two hundred and twelve degrees fahrenheit.
So these scientists in Singapore argue that the Impemba effect
comes from an interaction between the covalent bonds, you know,
(02:54):
the inner water molecule bonds, and the hydrogen bonds between
different molecules. Here's how they think it works. When water
molecules are close together, their natural repulsion causes the covalent
bonds to stretch and store energy. As the water warms up,
it becomes less dense, the hydrogen bonds stretch as the
(03:15):
molecules move further apart. When these hydrogen bonds stretch, they
allow the covalent bonds to shrink and release their energy.
This is equivalent to cooling. So according to the non
Young theory, hot water is essentially able to release energy faster,
leading to a quicker freeze. It's important to note that
at this point that work hasn't been peer reviewed, so
(03:36):
it's not a sure thing yet, but even if it's
just a contributing factor, it's a promising lead to a
question that's puzzled humanity for some twenty hundred years. Check
out the brain stuff channel on YouTube, and for more
on this and thousands of other topics, visit how stuff
works dot com.
Welcome to brain stuff from How Stuff Works. Hey, I'm
Christian Saga and this is brain stuff pop quiz. I'm
thinking of a substance. Let's see if you can guess
what it is. And it's pure form. It's odorless, tasteless,
and nearly colorless. It's in your food. In fact, a
(00:22):
lot of the stuff you use every day either contains
it or was manufactured using it. It's even in your body.
Can you guess what it is? If you guessed water,
then you're correct. Water is one of the most important
substances on earth as far as life goes, at least,
and it can do some weird stuff. For example, it
reaches a maximum density at around four degrees celsius and
(00:44):
then becomes less dense before it freezes. And here's another
strange thing. Hot water can freeze faster than cold water.
But why, Okay, this is a very old question. In fact,
Renee Descartes thought about it, and Francis Bacon before him,
Aristotle pondered the mystery too. Today we call this phenomenon
(01:04):
the Impemba effect, after a guy named Erasto Impemba, who
first observed the effect on ice cream when he was
just thirteen years old. His teacher, for the record, laughed
at him, Well who's laughing now? Turns out Rasto was
onto something big, and teams of experts would spend the
next few decades trying to explain why water behaves this way.
(01:25):
Scientists around the world cooked up dozens of theories, and
none were able to completely explain the process. But as
that may have changed. A research assistant at the University
of Zagreb in Croatia claims that convection currents in warm
water cause it to cool more rapidly, and the Royal
Society of Chemistry agrees with him. They actually gave the
(01:47):
guy a thousand pound prize for his experiments. But he's
not the only contender for a solution. A team of
physicists at the Non Young Technological University in Singapore took
the question to a much smaller level. They claim that
the answer lies in the bonding. Not you know, hanging
out with friends type bonding, but molecular bonding two kinds actually.
(02:10):
You see, every water molecule is made of two hydrogen
atoms bonded to a single atom of oxygen. These are
covalent bonds, which means that they share electrons between one another.
This is a chemical bond. Separate water molecules are bound
to their neighbors by weaker hydrogen bonds, which occur when
a hydrogen atom from one water molecule is close to
(02:31):
the oxygen atom of another water molecule. This is an
electromagnetic attraction and it's what gives water some of its
strange abilities, like it's unusually high boiling point of one
hundred degrees celsius that's two hundred and twelve degrees fahrenheit.
So these scientists in Singapore argue that the Impemba effect
comes from an interaction between the covalent bonds, you know,
(02:54):
the inner water molecule bonds, and the hydrogen bonds between
different molecules. Here's how they think it works. When water
molecules are close together, their natural repulsion causes the covalent
bonds to stretch and store energy. As the water warms up,
it becomes less dense, the hydrogen bonds stretch as the
(03:15):
molecules move further apart. When these hydrogen bonds stretch, they
allow the covalent bonds to shrink and release their energy.
This is equivalent to cooling. So according to the non
Young theory, hot water is essentially able to release energy faster,
leading to a quicker freeze. It's important to note that
at this point that work hasn't been peer reviewed, so
(03:36):
it's not a sure thing yet, but even if it's
just a contributing factor, it's a promising lead to a
question that's puzzled humanity for some twenty hundred years. Check
out the brain stuff channel on YouTube, and for more
on this and thousands of other topics, visit how stuff
works dot com.
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