What does the universal gas constant represent? [closed]

In the formula $$V=\frac{nRT}{P},$$ when we say $R$ is $\pu{0.082 L atm//mol K}$:

• What do we mean? Specifically what does $\pu{K}$ mean here? Also $\pu{mol k}$? and $\pu{L atm}$?
• Can you simplify it for a college level student who is taking a beginner course of chemistry.

closed as unclear what you're asking by Ivan Neretin, Klaus-Dieter Warzecha, M.A.R., Wildcat, Todd MinehardtMar 28 '17 at 13:59

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• Here K is the temperature in $Kelvin$ , mol K means moles Kelvin and L atm means Litre Atmospheres , they are respective units of the quantities in your formula. $n$= moles , $T$ in Kelvin , $V$ is Volume in litres and $P$ is pressure in atmospheres. – Piyush Raut Mar 28 '17 at 7:15
• Actually it's not like any relationship but it's the way to write the units of desired quantity like in this case $R$=$\frac{VP}{nT}$ so arranging your units for respective quantities we get $units-of-R$=$\frac{Litre-atm}{mol-Kelvin}$. I hope you got that. – Piyush Raut Mar 28 '17 at 7:43
• @PiyushRaut, I think what the OP is asking is what is the physical representation of R, i.e. where or what is it in real life? We know what a volume is, we know what pressure is, we know what temperature is and we know what quantity is, but what does this NUMBER that ties them all together really mean to us? Most people's immediate response would be: this is a "conversion factor" or a "constant of proportionality", but these are only mathematical definitions. In other words, can R be found anywhere in this world? At least, that's my interpretation, and I think it's a great question. – Don_S Mar 28 '17 at 8:27
• @Don_S I agree that would be a great question, and that was what I was hoping for when I clicked on the question. However, it seems that OP's real issue is over what the unit symbols of $R$ actually mean. (Note that the title is not OP's.) – orthocresol Mar 28 '17 at 9:16
• @Don_S I agree but the way the question was framed before being edited was like, related to units of the quantities mentioned . I agree it would have been really a good question if it would be something related to physical interpretation of Universal Gas Constant. – Piyush Raut Mar 28 '17 at 12:46

3 Answers

The universal gas constant arises because the units we use for the quantities in the ideal gas law (pV=nRT) are completely arbitrary. A harmonious set of units could be specified that allow R to be unity.

K is kelvin, the SI unit of temperature. It's based on the phase changes of water.

L is litre, or cubic decimeter

atm is atmospheric pressure

mol is the mole, defined as the number of atoms in 12g of carbon-12

• note that the mole is the amount of substance that contains the same number of atoms/molecules/ions as 12g of carbon -12. – porphyrin Mar 28 '17 at 11:28

Interesting question, I always assumed it was just a constant to adjust it to real values but there is also a formula for R I never head before. According to Wikipedia (if you trust these sources) R is also the difference of the heat capacity at constant pressure and constant volume and as we know R is the same for all ideal gases. So perhaps if you really want to describe and compare theoretical gases where you say they should behave ideal you don't want too much difference in your results once you change parameters like constant pressure or constant volume which is why you say this value, which might arise there is always the same for ideal gases but has to be included because we see that cp-cv is not equal to zero and therefore there has to be some, I just call it "intrinsic" property we have to add?

This would at least be my interpretation of this specific formula and the way how I would explain the necessity of having it to myself, like we assume an ideal gas has this perfect relationship where can bring volume and pressure together and easily calculate things but then suddenly we see that in fact keeping one of them constant causes differences in some thermodynamical calculations and we have to include something that corrects it.

Might be awefully wrong here though.

The $R$ is basically a empiric factor so that the formula gives you the right answer. The units are chosen so that the units in the formula are balanced. The $\mathrm K$ stands for kelvin (temperature).

I don't know where you got your definition of $R$ from, but in SI units it is $8.314\ldots\ \mathrm{\frac{J}{mol\ K}}$.

I would propose to always use SI units when possible.