LETTERS Amending the IUPAC Green Book To the Editor: The IUPAC has recently released the 4th edition of its puhlication Quantities, Units and Symbols in Physical Chemistry (the Green Book) (I).By and large, the IUPAC recommendations are reasonable, and we should do our best to follow them. Among the recommendations, however, there are afew whose logic could be tightened or which could he made more felicitous. Here is a list of suggested amendments to the Green Book. 1) Among the list of primary quantities, include that of entity (object, particle) with symbol ent. The dimensions of Avogadro's number and Boltzmann's constant would then be: NA ent mol-I
he J K-' ent-'
R = Nake J K-' mO1rl
Avogadro's number refers to a collection of 6.022 X loz3 "somethings" (objects, particles, etc.); for short, call the "somethings" entities. The product keT (e.g.) refers to the energy of a solitary "something"; for short, call that "something" an entity. 2) A,* = . . .kJ mol-I: replace with A@ = . . .kJ mol-set-' 3 3CO(g) + O,(g) = 3CO,(g) A p = -848.952 kJ mol-' (replace) 2
A p = -848.952 kJ mol-set-' The IUPAC recommendation for describing the change in a thermodynamic property accompanying a chemical reaction is too terse and elliptical: the "mol-I" label always triggers the question, "Per mole of what?" What we mean when we quote a figure such as the -848.952 kJ above is "for 3 rnol CO or for 312 mo102 or for 3 rnol C02" and we could (very tediously) indicate this b y . . . kJ (3 mol CO or 312 mol O2 or 3 mol Con)-', but that is just too cumbersome t o use. Alternatively, we could say, "For a unit increase in the extent of reaction variable", and could invent some symbolic way of showing that. I would prefer this route if it could he elezantlv - .done. As a compromise between "mol-I" (too terse) and "(3 mol CO or 312 mol O7 or 3 rnol CO9)-'" (too cumbersome), I suggest "mol-set-"', meaning therehy "for the set of stoichiometric numbers displayed in the indicated reaction equation". 3) Let the dimensions of the stoichiometric numbers v, appearing in a displayed chemical reaction equation he v, mol ilmol-set
in a manner analogous to that suggested by Craig (2).Then the dimensions for the terms in an equation such as
value of K depends on the choice of standard states. Trained chemists don't need a "reminder mark", and students will be confused by twovastly different uses of the same superscript symbol in one equation. The KO notation will only promote endless confusion; better to do away with it. 5) "amount of substance": replace by "particulate amount" The phrase "amount of substance" is cumbersome, and there have been many suggestions for replacing it by something else (3, 4). I like Kohman's suggestion of "particulate amount" (4). 6) "molar": replace by "particulatic" "Molar" is not a good word for "divided by amount of substance" ("dividedby particulate amount"). 1n grammatical form, "molar" signifies "of or pertaining to the mole" (see the denotation ofthe -ar suffix,as in solar, polar, circular, etc.), and (grammatically) "molar mass" signifies "mass per mole" and not "mass divided hy amount of substance." The IUPAC definition of "molar" thus tends to abet the alltoo-prevalent confusion of a quantity (amount of substance1 particulate amount) with a measure (number of moles) of that quantity. Let 1.00 X 1024 entities be called a blob. Then I think most persons would feel uncomfortable in reporting that the "molar mass" of silver is 179.126 per blob (179.126 g blb-I). This kind of salutary shock is unavailable to us because we use only one mensure-the mole-for reporting "amount of suhstance" ("particulate amountW),soit iaeasy to gloss over the unsatisfactory nature of "molar" t o mean "divided by amount of substance". As a corollarv t o mv suezestion of articulate amount" for "amount of '$ubsta;ce,'? suggest "particulatic" to mean "divided by particulate amount". With this usage we could say, for example, that the particulate volume of an ideal gas a t 0 "C and 1.01325 bar is 22.414 L mol-I
Vp = 22.414 L mol-I and that the particulatic mass of silver is 107.868 g mol-' (and is also 179.126 g blb-I, for that matter) mp = 107.868 g mol-I
7) "specific": replace by "massic" The word "specific" has other denotations as well as the one ("divided by mass") desired by the IUPAC. I think it better to give up this word and t o use in its place a word such as "massic" to mean "divided by mass," as suggested by a committee of clinical chemists (5). Then (e.g.) we could say of the constant-pressure heat capacity of COz(g) a t 25 OC and 1bar that the massic heat capacity c, is 0.8432 J K-I g-I, whereas the particulatic heat capacity C, is 37.11 J K-' mol-I: c, = 0.8432 J K-' g-'
A,Go = Z,u,A,G?
(or 179.126 g blb-'1
C,
= 37.11 J
K-' mal-I
would he kJ/mol-set
= 2,(mol ilmol-set)
(kJlmal i)
4) ArGo = -RTln KO: abandon KO and use only K The suggested introduction of a "standard equilibrium constant" KO should be abandoned. In the equation above, the superscript on the left-hand side means that everything is in its standard state, whereas on the right-hand side the superscript doesn't "mean" anything at all. I t is merely a "reminder mark", reminding the reader that the numerical 1064
Journal of Chemical Education
Llterature Cited I. Mills. I.; Cvifas, T.: Hnrnann, K.; Kallay, N.;Kuehitsu, K. Quantities. Units ond Symbols in Physical Ch~misfry:Blackwell: Oxford, 1988. 2. Craig. N. C. J. Chem Educ. 198'7,64.66&669. 2. Tykodi. R.J. J . Chem. Educ 1983,60,782. 4. Knhman,T. P. J. Chem.Edue. 1987.64.24fi. 6. ~ i g c .C.;VIPPOI, ~. B. F.: ~ e h m a n nH. . P.chemutrylnrernoriono1 1985,7(31.29-33.
Ralph J. Tykodi Southeastern Massachusem University N a t h Dartmouth, MA 02747
