Transcription
Here we're going to talk about how the hydrogen bonding that occurs in water, um, really impacts how water heats up or doesn't heat up very well. So, uh, we've already discussed how heat is really a measurement of how fast particles are vibrating or moving around in a substance, and the hotter something is, the faster the molecules are moving.
So here we have some water, uh, sitting in a container. Maybe it's a pan. Looks like it's a pan on a stove or on a fire, right? So, um, as this water heats up, what really happens are all these molecules in here are going to start moving around more and more and more. They start off just moving a little bit, and as they get warmer, they're moving, or moving, or moving until they're really moving fast.
Now, since all these water molecules are attracted to their nearest neighbors by all these hydrogen bonds, I like to think of these hydrogen bonds a little bit like bungee cords that are kind of holding these molecules in place. So obviously, the, um, more bungee cords you have, the harder it is to move around. If you're kind of strapped down by four, four hot bungee cords holding you to your nearest neighbors, and then they're strapped together with four more bungee cords, it's hard for you all to get moving.
And so what this is saying is that you've got to put a lot of heat into this, into this collection of molecules, into this collection of water molecules to get them to move, because they've all got to overcome lots and lots of bungee cords which are holding them back. Because every single water molecule, even though it's tiny, you can make four hydrogen bonds, or has four bungee cords strapping it down, so, so holding it in place.
And so, uh, it takes a lot of energy. You've got to put a lot of heat into water to get these molecules to move around. Um, and so what that means is, well, two things, I guess. You can think of it in many ways. Number one, you've probably heard the saying that a watch pot never boils, or it takes a long time to heat up water on the stove, even though the stove is red hot and if you touch it, you burn yourself. The water just sits there and takes a very long time to get to boiling. And that's reflecting this. It's reflecting the fact that the molecules are having a hard time getting moving because they're so attracted into, into position.
So that's the one thing. Uh, now that it may be a pain in the, in the kitchen when you're trying to cook pasta quickly, it takes a long time to boil the water, but it is really helpful to us on planet Earth because we have a lot of water, um, on our planet. Right, 70% of the surface of the, of the Earth is coated in water, all these oceans.
And so, uh, here's an example. If you go to San Diego in the wintertime in December, uh, and you go in the ocean, it's about freezing cold, right? That ocean is really, really, really cold in the wintertime. Um, so you come home, right? You go back to San Diego in August, and the sun has been shining on the ocean for 10, 12, 13, 14 hours a day for four months straight, and the sun is hot, the beach is hot, it's really, really hot. You get in the ocean and it's still pretty, but freezing cold out there. Because it's a big ocean, it's a big amount of water, and even though the sun has been shining on it and putting heat energy into it for months, for hours on end, and it's a hot sun, the water still doesn't get that much hotter. It gets a little bit warmer, obviously, but it doesn't get super, super, super warm. Nowhere near as warm as the sand does, all right?
So that is really, really good for our planet because what it does is it stops the temperature of our planet from, uh, wildly going very, very, very hot when the sun's out and very, very, very cold when the, when the sun's not out. Having water to absorb all that energy from the sun without the temperature going up very much keeps our climate much more stable than it otherwise would be.
If you've ever seen that movie, uh, The Martian, where Matt Damon's living on Mars, right? Um, and Mars doesn't have any liquid water anymore. You may have had in the past, but there's no water there now. Um, when the planet rotates and the sun shines on it, it's super, super, super, super hot because the sun is putting all that energy into the rocks, and the rocks heat up real easy. And then when the, when it rotates away from the sun, all of a sudden the temperature plummets and it gets really, really cold very quickly. And that's because there's no water there to absorb the heat energy and not raise the temperature. The rocks absorb the heat instead, and it gets hot real quick.
And that's what we see here in the desert, actually. We don't have a lot of water. There's not a lot of humidity in the air. And so when the sun is out, it feels very, very, very hot. But when the sun is not out, in the wintertime, it can drop down almost to freezing. We get this wide temperature. We get as bad as a wider temperature range as you can have on planet Earth in the desert. It can be as hot as 120. It can get down to freezing. And that's because we don't have much water around to buffer those changes in temperature.
Somewhere on the coast, in the coast of California, it's never very, very, very hot. It's never very, very, very cold. It's kind of in the middle, and it goes up and down a little bit, but nowhere near the big extremes that you see in more drier places, or the extreme extremes you see on drier planets like Mars.
So without this amount of water and without the ability of water to absorb all this energy from the sun and not get hot very easily, our planet would be very unstable, and our climate would be super erratic and probably too diverse for life to survive. But because we have lots of water on our planet, the temperature is pretty stable compared to most places, um, and so life can make it and life can make it through the seasons because it's not super, super different between winter and summer compared to what it's like on somewhere like Mars.
So I'm going to move to this next slide here, give you a little example. So here is, um, an example of something called specific heat. So here I have a collection of water molecules. We're saying this is one gram of water. Now, really, a gram of water, that would be like a little drop in my palm of my hand. It would be bajillions more molecules than the six I'm showing here, but it's just an example. This is a gram of water at five degrees. So that's not very warm. These molecules are moving a little bit, but not very much. And I'm going to heat these molecules up from five degrees to six degrees, which means I'm putting, I'm making them move a little bit faster. See, they're only moving one arrow here, one hour of jiggling here. They've got two arrows of jiggling, so they're moving a little bit faster down here, and that means they're now they're at six degrees, whereas before they were only five degrees.
The amount of energy that I had to put in to make them move faster, the amount of heat it took, is what we call a calorie. This is the same kind of calorie that's in food. It's a measurement of energy. As this is the official definition, the amount of energy you put in to water to raise one gram of water by one degree Celsius from five to six. All right. And remember, remember these all these water molecules are being held to their neighbors by lots and lots and lots and lots of hydrogen bonds, and that's what's holding them still and making it hard for them to jiggle faster. All right. So this is water. Now, and water has four H bonds per molecule, which is what this diagram up here shows, shows.
All right, down here I've got a different molecule, and this is ethanol, which is drinking alcohol, what's in a beer and vodka and wine and stuff. So this is ethanol. Ethanol also makes hydrogen bonds, but it's a slightly bigger molecule than water, and it only makes roughly two hydrogen bonds per molecule because only this end part right here can actually make hydrogen bonds. It's that's the only part that has a charge. So while ethanol is a larger overall molecule, it's got way more atoms in it. Look, there's a, there's an ethanol molecule. This out, this ethanol could only make two hydrogen bonds. This one's making a bond up here and up here, down there. This one would have one this way, maybe over here to something else. So less hydrogen bonds between these ethanol molecules than there would be if there was water molecules involved.
So if I take the same amount of energy, one calorie, one calorie's energy will move water from five degrees to six degrees in terms of temperature. If I have the exact same amount of energy, one calorie, and I have ethanol at five degrees, and I put one calorie of energy into here, will the temperature of the alcohol go to six degrees? Will it go to less than six, like maybe only makes it a five and a half? Or will it make it to more than six, maybe it'll make it to six and a half or seven? For the same amount of energy. So I have the same amount of, I've got alcohol in this hand, and I've got water in this hand, and I'm going to put the same amount of energy into both drops of liquid. The water will go from five to six. What will happen to the alcohol? It will go from five to what? What do you think? I'll give you three seconds.
All right, so based on the fact that there are four bungee cords holding these water molecules in place, and the energy makes this go from five to six, the alcohol, there's only two bungee cords holding these molecules in place. So if I put the same amount of energy, and they're going to be able to move easier because they don't have as many bungee cords holding them together. So instead of going from five to six degrees, this is gonna go from five degrees, maybe up to six and a half or even seven degrees. It's going to get warmer for the same amount of energy put in because I can make these molecules move faster, easier.
All right, I'm going to let you think about that and consider if you can make sense of that in your brain.