Allen wrote:
Fifty years ago, I could have calculated the volume of gas given off by
> one gram of oxalic acid dihydrate in a jiffy, and probably found the heat
> of fusion and the heat of vapourisation of the dihydrate, too. These days,
> I'm a bit rusty.
>
> I'm betting we have some chemistry whizzes reading who could offer
> assistance.
>
I am not a whiz, but can offer this: The volume depends on the pressure
and temperature as well as the molecular weight of oxalic acid dihydrate.
The gas law formula is PV=nRT so V (volume) = n (avogadro's number, 6.02 x
10 to the 23) x R (molecular weight, or weight of one mole of oxalic acid)
x T (temperature, in degrees kelvin) / pressure (in this case atmospheric
pressure, in units suitable to give you the volume in units you want).
I think you can assume that blocking big cracks in the hive still does not
appreciably raise atmospheric pressure, and you are not so high there in
Alberta (although higher than PEI).
But the temperature to use for the calculation is problematic. I would
suggest that you use the melting point of oxalic acid, although it would be
higher initially and lower subsequently. Add 273, I believe, to celsius to
get kelvin.
To show you how rusty *I* am Allen, before I posted the above I said to
myself is R the number of moles or the molecular weight. Turns out it is
neither and I had the n and R reversed and the constant was not right
anyway for the units. Here is the correct ideal gas law (and if you use
the constant from the first version, you can use 1 for the pressure in
atmospheres, and calculate the moles from the grams and molecular weight of
oxalic acid):
With the addition of Avogadro's
law<http://en.wikipedia.org/wiki/Avogadro%27s_law>,
the combined gas law
<http://en.wikipedia.org/wiki/Combined_gas_law>develops into the ideal
gas law <http://en.wikipedia.org/wiki/Ideal_gas_law>:
[image: PV = nRT \,]
where
*P* is pressure*V* is volume*n* is the number of moles*R* is the universal
gas constant*T* is temperature (K)
where the constant, now named R, is the gas
constant<http://en.wikipedia.org/wiki/Gas_constant>with a value of
.08206 (atm*L)/(mol*K). An equivalent formulation of this
law is:
[image: PV = kNT \,]
where
*P* is the absolute pressure*V* is the volume*N* is the number of gas
molecules*k* is the Boltzmann constant (1.381×10-23 J·K-1 in SI
units)*T*is the temperature (K)
These equations are exact only for an ideal
gas<http://en.wikipedia.org/wiki/Ideal_gas>,
which neglects various intermolecular effects (see real
gas<http://en.wikipedia.org/wiki/Real_gas>).
However, the ideal gas law is a good approximation for most gases under
moderate pressure and temperature.
This law has the following important consequences:
1. If temperature and pressure are kept constant, then the volume of the
gas is directly proportional to the number of molecules of gas.
2. If the temperature and volume remain constant, then the pressure of
the gas changes is directly proportional to the number of molecules of gas
present.
3. If the number of gas molecules and the temperature remain constant,
then the pressure is inversely proportional to the volume.
4. If the temperature changes and the number of gas molecules are kept
constant, then either pressure or volume (or both) will change in direct
proportion to the temperature.
Happy Earth Day
Stan
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