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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: confus3d on September 26, 2007, 06:12:59 PM

Title: Why is the universal gas constant 0.08206?
Post by: confus3d on September 26, 2007, 06:12:59 PM

How was that derived? by whom?
What were the calculations?

Title: Re: Why is the universal gas constant 0.08206?
Post by: Borek on September 26, 2007, 06:44:28 PM

It is determined experimentally.

0.08205783 L*atm/(K*mol)
8.314510 kPa*dm3/(K*mol)
8.314472 L*kPa/(K*mol)
8.314472 J/(mol*K)
62.3637 L*mmHg/(K*mol)
83.14472 L*mbar/(K*mol)
1.987216 cal/(K*mol)

Title: Re: Why is the universal gas constant 0.08206?
Post by: pantone159 on September 27, 2007, 02:59:53 AM

Another way of looking at it, is that the 'gas constant' is Boltzman's constant, k, from statistical mechanics, times Avagadro's number.  R = k * Na.  (Physicists like to count by single things, chemists like to count by moles.)

How the value of k is determined, I leave as an exercise for the reader.  :)

Title: Re: Why is the universal gas constant 0.08206?
Post by: billnotgatez on September 29, 2007, 07:29:51 PM

If you treat this as an algebraic problem it seems somewhat clearer.

PV=nRT is rearranged to R=PV/nT
You also know that 1 mole has a finite volume at standard temperature and pressure
1 atmosphere pressure
273.15 K temperature
1 mole
Approximately 22.4 liters (let us use 22.4140962645)
Therefore 0.08205783 = 1 * 22.4140962645 / 1 * 273.15

I think that the confusion comes in when you use just 22.4 and get a slightly different value for R.