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What are the Properties of Liquids? Surface Tension, Viscosity, Special Properties – Chemistry Tips


In this video, I’ll talk about the properties of liquids — specifically, the surface tension, the viscosity, and the special properties of water. Now, the definition of the surface tension is “the amount of energy required to stretch or increase the surface of a liquid by a unit area.” So we have a water strider here, to give an example of this. This water strider is kind of floating or using the idea of surface tension to help it stay on top of the water. And here’s what’s happening. If you have all of these water molecules, they are all bunched together, and you’ve got a glass full or a lake full of these water molecules. Well, there is a force holding these these water molecules together. Now, these intermolecular forces… Now, if we bring some force down, and we’re talking about surface tension as the amount of energy required to stretch or increase the surface of a liquid by a unit area. So, that is how much energy or how much force do we need so that these molecules will start to pull away from each other so that we can we can go right through the surface of the water. Well, the water or other liquids, the surface tension is different for different liquids. Here we see a water strider on the liquid water, so that’s the idea of surface tension. Now, viscosity. Viscosity is a “measure of a fluid’s resistance to flow,” a measure of a fluid’s resistance to flow. So, I have a picture of oil here, and you can think of it. It could be oil. It could be molasses. It could be a lot of things that you think of when we think of viscosity. Oil is a good one because when we put oil in the car and the engine heats up, then the oil is going to flow much faster when the temperature gets higher. In fact, the greater the the viscosity, the more slowly the liquid flows. So higher viscosity, the liquid flows slowly, and the viscosity of liquid usually decreases, usually decreases, as the temperature increases. So, you’ve heard of this comment “slow as molasses in January.” Well, that’s we’re talking about. It’s a nice chemistry “joke” is what it is. It’s talking about as molasses gets colder in January, it is more viscous and, therefore, flows more slowly. So the higher the viscosity, the slower it flows. And the higher the temperature, as the temperature increases… Let’s say that this is a thermometer, and as the temperature increases, then the viscosity decreases. And this fluid, whatever it is — oil or molasses or even water — the fluid will flow faster. So that’s an idea of viscosity. Water is very special because its solid form floats, which is really kind of amazing. Whether you know it or not, most compounds in their solid state are more dense than their liquid state, but water floats. Now, you may have heard that it’s because water ice has air trapped in it. Well, let me clarify this. It is true that most ice gets air trapped in it, but that is not the only reason that ice is less dense than liquid water. Even if you are able to form a perfect block of ice without any air trapped in there, it would still float on water. And the reason is because the molecular forces, the intermolecular forces, and the hydrogen bonds that bond the the water molecules together in the solid form, they get very large, and that’s just kind of a quick way to describe it. The water molecules are farther apart when they are in their solid state, and therefore, you have fewer molecules per volume and so it is less dense. So there’s just some introduction on the surface tension, viscosity, and some special properties of water. I hope you found that helpful. If you did, consider liking it or sharing it with a friend.

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