Here are the example question states using the van der Waals equation, determine the pressure of 20 grams oxygen gas in 250ML graduated flask when the temperature is 50�C. All right, so we're going to say the Van der Waals equation is
P + N 2 A V 2 ( V - N B ) = N R TNow all we got to do is plug in the values that we have.
So we need to have the moles of oxygen O. Remember, oxygen is diatomic, so one mole of O2 weighs 32 grams O2. So when we do that, we're going to get our moles up. O2 comes out as 0.625 moles of O2. Volume has to be in liter, so that's 0.250 liters. And then temperature needs to be in Kelvin, so add 273.15. That gives us 323.5 Kelvin.
Since we're dealing with O2 in the chart up above, we would see that the A constant it comes out to 1.360. The B constant comes out to 0.0318. With this information, we plug it into the formula. All right, so let's see. We're looking for pressure, so we don't know it. So this is going to be, oh,
0.625 2 * 1.360 / 0.250 2And this is going to be times volume which is 0.250 minus moles which is 0.625 * 0.0318 and this is going to equal my moles R&T.
So moles I'm going to actually move all this out of the way so we have space to write this out. So here our moles again come out to 625, so the van der Waals equation related to the ideal gas law. So R again is 0.08206 and then temperature is 323.15 Kelvin. When I multiply these three together on this side, it comes out to be, let's see, we're going to multiply those out together. That comes out to be 16.57356.
When I when I do this value minus these two multiplying what I get is I'm going to get 0.230125. Then when I work all of this out in here, this comes out to be 85 plus P So now I need to isolate my P So I'm going to divide both sides here by 0.230125. So P + 8.5 equals 72.00. Subtract 8.5 from both sides so P = 63.5 atmospheres, so that would be the pressure of O2 when utilizing the van der Waals equation.