00:01
Okay, this is chapter 11, section problem 108.
00:05
The vapor pressure for pure water and pure acetone is measured as a function of temperature.
00:11
In each case, a graph of the log of the vapor pressure 1 over t is found to be a straight line.
00:18
The slope of the line for water is minus 4895k, and the slope of the line for acetone is minus 6748k.
00:29
Determine the hvap or the heat of vaporization for each substance account for the differences by discussing the molecular structure of the two molecules.
00:41
Okay, so if you look in the book, in example, 11 .4, you know, it provides, you know, the kind of graph that probably these students were attempting to make.
00:57
And it's derived by the clausius clapperon equation.
01:02
And essentially, as it was saying, if you plot the natural log of p versus 1 over k, you get a line, you take the slope of that line.
01:12
And then essentially, the slope times r is equal to minus the heat of vaporization.
01:20
Now, if you plug the numbers that you gave, they gave us.
01:24
And we get a heat of vaporization for water of 40 .40 .7 kilojoules per mole, and using the numbers they gave us, you get a higher heat of vaporization for acetone, 56 .103 kilo -joules per mole or whatever.
01:45
That's ridiculous, and it's impossible, and i'm not sure if it's a typo or if the textbook is intentionally trying to throw us off.
01:55
It's one of the two.
01:56
If you go on wikipedia real quick, you know, you see that in fact, yeah, it does, you know, water has a higher heat of vaporization than acetone.
02:08
And i'm sure if you looked into more reputable sources or, you know, literature too, you'd get the same answer.
02:13
And water really necessarily is going to have, you know, more energy required to break, you know, go from liquid to a gas phase because it has, way more intermolecular stronger intermolecular forces of attraction because water can hydrogen bond and acetone can.
02:32
So, you know, it's a huge red flag that they calculated a higher value for acetone than for water because it just doesn't make sense.
02:44
I plugged into the equation real quick, like, well, what if they, you know, what if they copied it down wrong? it's supposed to be a 3748 instead of a 6 -748.
02:55
And that gives you something way closer to the answer this on wikipedia.
03:01
It could be that the textbook writers just wrote that down wrong.
03:05
Or again, maybe they're trying to suggest that the students made a mistake in the experiment, which is also possible...