On 15 January 2012 22:32, Chris Smith <[email protected]> wrote: > On Mon, Jan 16, 2012 at 2:45 AM, [email protected] > <[email protected]> wrote: >> I have two problems with this. First of all mol is not a number as >> dozen. It's a measure of quantity of matter. The idea was created >> before the atomistic theory of matter and the only important property >> is additivity. You use the Avogadro's constant (again not a pure >> number) to connect the two. So to use mols you don't need to know that >> matter is made of discreet particles. > > Quoting from NIST: > > "The mole is the amount of substance of a system which contains as > many elementary entities > as there are atoms in 0.012 kilogram of carbon 12; its symbol is "mol."" > > This is clearly a number, isn't it? No, it's an "amount" as defined by SI. It's one of the basic units. > > When you divide a mass by a mass you should get a number. It is > arbitrary what lumped number you want to report that in: million, > dozen, mol....so I think mole is ok as a number unit. But since no > other dimensinally cancelling ratio will be reported in anything but a > number, we should be consistent. So... > > If we use amu = g/6.e23 then g/amu gives 6e23 and g/amu/mol will give > 1. If we defined dozen=12 then foot/inch/dozen would also be 1. yes, g/amu = avogadro, not mol > > And we leave avogadro as it is. Yes > > Sound ok? Ok for leaving avogadro as it is. Not ok for changing mol to be a number.
But there is no need to argue if "amount" is a number or a unit. If we define mol = avogadro as you propose how will one represent 1mol. When he writes 1*mol he will get printed a long number, not "1*mol". Even if I'm wrong about the definition of Mole in SI, making mol a number in sympy will not permit the symbolic expression x*mol (it will always be evaluated to 6.....0000000*x, Mul will not treat mol specially). avogadro and mol are correctly defined as they are at the moment in sympy. Only amu was wrong. You mention a few times that the correct definition makes the use of molar mass as amu difficult because one must multiply by mol. Well, we may add some helpers, but I don't think that ease of use is more important than correctness. Concerning "amount": from nist http://physics.nist.gov/cuu/Units/mole.html "Unit of amount of substance (mole)". A unit, because "amount of substance" becomes "number of atoms" only if you know that matter is made of atoms. The usage of Mole was started before atomistic theory. That's why it's a unit. > > -- > You received this message because you are subscribed to the Google Groups > "sympy" group. > To post to this group, send email to [email protected]. > To unsubscribe from this group, send email to > [email protected]. > For more options, visit this group at > http://groups.google.com/group/sympy?hl=en. > -- You received this message because you are subscribed to the Google Groups "sympy" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/sympy?hl=en.
