Should compounds in a generic reaction be italicised (typography)?

Question

As of recent, I provided an answer to the question Law of mass action & collision theory. Therein I wrote a generic reaction

$$\ce{$r_1$R1 + $r_2$R2 + \ldots + $r_n$R_n <=> $p_1$P1 + $p_2$P2 + \ldots + $p_m$P_m}.\tag{1}$$

It seemed natural to write stoichiometric coefficents in Italic, and use upright Roman for the species themselves.

• Italic would be in line with the fact that the coefficients are numbers, and vary with reactions (are different for different transitions).
• Upright Roman is how we usually write chemical species, e.g., $\ce{NaCl}$.

Though if I were to overthink, the $\ce{R_$i$}$ would also seem to be variables as such. Since this is a generic reaction, $\ce{R_$i$} \in \{\mathrm{every\ imaginable \ chemical \ species}\}$. Using this logic, I ought to write $(1)$ instead as

$$r_1R_1 + r_2R_2 + \ldots + r_nR_n \ce{<=>} p_1P_1 + p_2P_2 + \ldots + p_mP_m.\tag{1'}$$

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• Is there an official example or guideline how to handle this situation?

Personally I wholeheartedly support option $(1)$ but is this what is recommended?

• What about the subindices? Upright or Italic?

Note that this qualitatively differs from Proper typography of “$\ce{NO_x}$”. There the number of elements actually changes within a chemical species (marks the number of carbons in alkanes for example) whereas here it is more for labelling purposes.

Answer 1

Going by the basic rule of a variable (that can hold multiple values) being italic, I would go for the $r_nR_n$ style (4 times italics), but then I found the following in the IUPAC Green Book (printed page 53):

$$0 = \sum_j \nu_j \mathrm{B}_j \quad \text{where }\mathrm{B}_j\text{ denotes a species in the reaction ...}$$

Here, the B is upright although it is definitely a placeholder. I don't understand, why.

For the subindices, I think (hope) there is no doubt that the $n$ and $m$ should be italic, because they clearly are variables standing for numbers (either any number as in the sum, or for an unknown maximum number $1, 2, 3, \ldots, n$ as in the generic reaction). Both form are well established in mathematics (and I hope chemists don't deviate).

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The IUPAC Gold Book, R05156 uses the same convention.

For the general chemical reaction : $$a\,\mathrm{A} + b\,\mathrm{B} \rightarrow p\,\mathrm{P} + q\,\mathrm{Q} + \dots% not using \ce to have proper formating regardless of mhchem version$$

And they do not mean Boron and Phosphorus.

(Spotted via this answer).