I'm making a latex to speech library, and I have come across


which looks like this:

which is in context to this equation:

\rm CO_2 + H_2O \rightleftarrows H_2CO_3 \rightleftarrows HCO_3^- + H^+

I tried looking for the symbol in Larry's speakeasy, which is a guide to verbalizing math, but that symbol was not in there.

Rather than simply saying, Right Left Arrows. , is there better terminology for this symbol?

  • 5
    That's the wrong arrow for the context: you want an equilibrium arrow, which is 'half' in each direction
    – Joseph Wright
    Feb 3, 2017 at 8:20
  • 5
    Yes: my 'day job' is as a chemistry lecturer!
    – Joseph Wright
    Feb 3, 2017 at 8:22
  • 4
    On the arrows business, chemistry.stackexchange.com/questions/20127/… covers it (though it's very rare to see ). On the main part of your question, I have a feeling it's off-topic as it's not really TeX related. For a chemistry context you'd read the equation as something like 'carbon dioxide plus water is in equilibrium with carbonate and protons'.
    – Joseph Wright
    Feb 3, 2017 at 8:31
  • 1
    chemically speaking, "reacts in both directions" is not entirely wrong, but the proper terminology is still "in equilibrium with"
    – Xylius
    Feb 3, 2017 at 9:24
  • 2
    Taking into account some of the comments on your previous related question I think you're going to end up needing a significant option on this library: What it's talking about, e.g. Chemistry/Physics/Maths (you'll almost certainly need to subdivide at least some of these) as a particular symbol's meaning will differ (even if used properly e.g. \rightarrow, but more significantly they're not always used properly . I suggest a "read the symbol name" variant as well (even if you decide not to implement field-specific meanings yet)
    – Chris H
    Feb 3, 2017 at 9:48

1 Answer 1


The equilibrium arrows you show for chemical equations usually look like this:
enter image description here which can be displayed using \leftrightharpoons

For your purposes of speech to text, while using "reacts in both directions" is not entirely wrong chemically speaking, the proper terminology is "in equilibrium with"

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