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# Units of the universal gas constant - Jk-1mol-1 Watch

1. why mol^-1 ?

PV=nRT

re-arranging to make R the subject, you get R = PV/nT.
In terms of units:
P*V = nm = J
PV/T gives JK^-1
And PV/Tn gives JK^-1mol^-1.

So this implies that the number of moles has units - moles.
I thought it wouldnt as it just seems like quantity/number to mee

hmmm
2. It just depends whether you are doing units per mole or not:

PV = RT (use 287 for air) OR PV = nRT (use 8.314)

Both are equally valid but it depends what the question is asking.
3. I suppose as a unit, it is slightly strange, as it is just referring to a fixed number of molecules/atoms/ions/etc.
However it is much more convenient to refer to 0.8mol, than 0.8x6.02214x10^23 or whatever.
4. (Original post by Van_der_Waals)
I suppose as a unit, it is slightly strange, as it is just referring to a fixed number of molecules/atoms/ions/etc.
However it is much more convenient to refer to 0.8mol, than 0.8x6.02214x10^23 or whatever.
mmm yeh, but when u express the equation as PV=NkT, where k is boltzman constant, its units are Jk^-1, like you dont say x joules per kelvin per molecule, whereas with R you are saying x joules per kelvin per mole... lol

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Updated: December 12, 2010
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