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Generally, is it better to work in metres-cubed or litres in chemistry?

My undergraduate degree was in civil engineering and we always worked in $\mathrm{m^3}$.

However, I notice the gas constant $R$ is used in a few different forms:

$$R=0.0821\mathrm{\frac{L\cdot atm}{mol\cdot K}}$$ $$R=8.3145\mathrm{\frac{J}{mol\cdot K}}$$ $$R=8.2057\mathrm{\frac{m^3\cdot atm}{mol\cdot K}}$$

among others.

I guess it depends on the application but is it generally easier to work in litres or metres-cubed?

Jan
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K-Feldspar
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    In chemistry, I have only ever used $\mathrm{\frac{J}{K \cdot mol}}$ for $R$ and only ever litres for volumes. – Jan Jul 07 '16 at 04:16
  • Generally for calculations involving R where I'm given a table of R values, I use the units that are the easiest to cancel out. I agree with Jan that litres are typically the only thing I use practically; the only real reason for metres-cubed are those general chemistry unit conversion problems. –  Jul 07 '16 at 04:57
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    In chemistry, unlike engineering, volumes are usually reported in dm$^3$, rather than m$^3$ such as mol.dm$^{-3} $ for concentration and dm$^3 $.mol$^{-1}$. s$^{-1}$ for second order rate constants. – porphyrin Jul 07 '16 at 07:32

2 Answers2

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Values for the gas constant are tabulated for various different units as a matter of convenience, since when carrying out calculations, the units of the gas constant need to match out with the other values being used (which in turn depends on the expression being used in the calculation) and its often easier to look up a value of the gas constant than to convert everything else into a specific set of units.

Generally, chemists aim for SI units, however there is a great deal of discrepancy between, for example, chemists in the USA vs. chemists in Europe. This is especially apparent in physical chemistry.

For example, the SI unit for energy (+work, +heat) is joules, such that the 'correct' way would be to express energy is terms of kJ/mol or J/mol, however, for historical reasons, many american chemists still work in calories (ending up with kcal/mol etc).

In terms of the volume question, we have equally confusion.

For small quantities, volumes are measured in units like millilitres, micro litres etc, though cubic centimetres (CC) do occasionally get used. For calculations involving moles/concentrations however, we default to decimetres and metres cubed. (you should note that 1 decimetre cubed == 1 litre)

In conclusion, in an ideal world we'd all use SI units, but various quirks have meant that we don't. If in doubt, look at what other people in the literature are doing, and, whatever units you choose, make sure that the units in your calculation match up.

NotEvans.
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    Of importance is the fact that the litre is a more convenient unit for the bench chemist whose daily work typically involves smaller scale solutions and reactions. The cubic meter (= 1000 L) is more convenient for the chemical engineer because it likely more closely matches the scale. – Ben Norris Jul 07 '16 at 14:23
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The units depend on the context that you are using at the present moment. We generally perform most calculations in SI units hence, cubic meters is preferred, unless everything that you are dealing with is not in SI units.

Tanmay Kulkarni
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