Van der Waals Equation

by Jules Bruno
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now remember that the Vander Waals equation is used for real gasses. You'll notice that there's no purple box because you're not expected to memorize it. If you do have to use it on an exam, it's usually embedded within the question or on a formula shoot. So if we take a look here, we say that for the Vander Waals equation, it is pressure, plus your moles squared times your vander wal's constant a divided by your volume squared because this portion contains Are Vandals constant? A. It is a correction for attractive forces or just the polarity. General polarity of gas molecules. Then that's gonna be times volume minus your moles and times your Vandals constant be because B is involved here. This is a correction for the volume off gasses, which could be tied to their size. Now this equation may not look like it, but it's connected to your ideal gas law. The Van Waals equation is used for real gas is the ideal gas law is used for ideal gas is but ideal. Gasses are imaginary. If ideal gas has existed popular, one says that their volume is so small that it's insignificant and not important. It's negligible, so sense they're so small. That means their size would be equal to zero. Let's look if if event, if an ideal gas is involved, be a zero so end times zero is zero. This would mean that this entire part here is just V. And then if we're dealing with an ideal gas and ideal gas has completely elastic collisions, it has no attractive forces or repulsive forces, so it's polarity would be equal to zero. So take that zero and plug it in. So n squared times zero divided by the square, all that just become zero. So all you have left is P. So if we're dealing with an ideal gas, the Vander Waals equation becomes simplifies into the ideal gas law. So that's the connection. They have to one another. Now, if we take a look here at the columns we have, all these gas is the second column. Are are a values and they're in units of atmospheres. Times leader squared over mole squared. And then here we have beat, hear their units are leaders over moles with polarity, attractive forces. It's harder to see a pattern. But remember be is our size coefficient, we said, as the molecular weight increases your value for B increases. So if you were to look and look at all the weights of each of these gasses, it would make sense in terms of the numbers, as as you see them more or less. There's a few deviations, of course, because it's chemistry. But the general trend is, as you increase the weight of a gas, you should see your B value increase as well. All right, so that's how our Vander Waals equation is connected to the ideal gas law. And this long equation is the Vander Waals equation. Again. Don't worry too much about memorizing it. It's more important to understand the ideas of the coefficient A and B.