Notes from Professor Boggs:
I remember how massively confused I was about the Ideal Gas Law upon first hearing it, and how ridiculously simple it all seemed later. That’s a good sign of a teaching problem (or a learning problem, I suppose). It seems like a lot of “magic numbers” at once, and perhaps that’s why teachers often just teach Boyle’s and Charles’ laws. But they don’t have as interesting names, which is a real problem for a songwriter.
So this is as simple as it gets. 22.4 liters of gas at STP in a box. One happy Avogadro mole, and let’s ignore the units of measurement. Squeeze it and it pressurizes…or it burps. Believe me, after this song, your students WILL have the formula, even if they don’t fully understand it.
Subjects for post-review: the meaning of a “mole” of gas (one gram times its atomic weight, which always ends up being the same number of molecules), the various expressions of “R” for different units (have a scavenger hunt!) and how to throw the equation around into different shapes (index cards with the symbols P, V, =, n, R, and T can illustrate this well).
At the end I hint around at the link to Newton’s laws of motion, which can, in fact, be used to derive the Ideal Gas Law. May be a bit advanced for most curricula, but please don’t ignore your math geeks…
Verses
Hey Avogadro – give me a mole – I need
Just enough gas to fill a cubical hole
It’s got twenty two point four liters inside
But for temperature and pressure you got to be my guide
Avogadro
You got the number you see
You sayin’ P V equals n R T
Thanks Avogadro (you got it)
You know a hot gas is gonna wanna expand
That’s why the volume and the temperature
they go hand in hand
But now the pressure goes up
when you shrink the volume down
It’s called an inverse proportion –
It’s kind of turned around
I know that R – has got ya confused
It’s just a number we pulled cause of the units we used
Don’t got to learn it – you can find it in a book
Or you could put it in your memory
so you don’t have to look
I’m heatin’ up that gas in a box of fixed size
The problem is I don’t want my pressure to rise
What do I do? The only number left is n
I gotta lose some gas – that baby’s got to vent.
Each molecule of gas is like a little rubber ball
Bouncin’ back and forth, puttin’ pressure on the walls
The temperature will tell how fast they gotta move
And if you do the Newton math you get the Avogadro groove
Hey Avogadro – give me a mole – I need
Just enough gas to fill a cubical hole
It’s got twenty two point four liters inside
But for temperature and pressure you got to be my guide
Avogadro
You got the number you see
You sayin’ P V equals n R T
Thanks Avogadro
Six point oh two two e x p twenty three
Comments
What’s a mole? Well, it’s basically the number of atoms in a gram. Except that different elements weigh different amounts, and we want a mole to always be the same number of atoms, so it’s really the number of atoms it takes to make up a gram times your atomic weight. So if you’re Carbon-12, weigh out 12 grams and you got a mole of Carbon. Ok? If you’re a mole of gas, and you’re at sea level and room temperature (standard temperature/pressure or STP), you fill up 22.4 liters. Ok? Doesn’t matter which gas you are!
Yep, raise the temp and the gas gets bigger! Either that, or the pressure goes up! So, see, a bigger T means a bigger V (that’s called DIRECT proportion), or a bigger T means a bigger P (DIRECT again), or if you SQUEEZE it smaller the pressure rises – smaller V means bigger P (an INVERSE proportion). Avogadro say:
PRESSURE times VOLUME follows TEMPERATURE.
