Is it somehow possible to change the default length of arrows in chemical reactions using mhchem? In particular I would need to reduce its length, both for single and for double (equilibrium) arrows. I ask, if possible, coherent solutions, in the sense of commands designed for this package, if they exist. I tried something like \ce{a + b ->[-5pt] c}, it seems to not work

  • This post says how to make double arrow longer? Have you seen this before? – Majid Abdolshah Mar 29 '19 at 1:58
  • Yes, I saw it. But I need something in order to reduce it, not to make it longer – TFra6 Mar 29 '19 at 10:27
  • The author of mhchem replied and said “I am quite busy at the moment, but I will eventually implement your suggestion.” – egreg Apr 2 '19 at 8:56

The package doesn't provide a way to set the minimum arrow width, but it's possible to add it.


\keys_define:nn { mhchem }
  arrow-min-length .code:n =
   \cs_set:Npn \__mhchem_arrow_options_minLength:n { {#1} } % default is 2em


\ce{A + B -> C}

\ce{A + B <-> C}

\ce{A + B <=> C}


\ce{A + B -> C}

\ce{A + B <-> C}

\ce{A + B <=> C}


enter image description here

You can use \mhchemoptions{arrow-min-length=1em} in the preamble to set the length globally, or locally in some environment.

| improve this answer | |
  • I was to the pag. 18 of mhchem package and I was not understood the code \mhchemoptions{arrows=% pgf{Kite[length=0pt 4,width’=0pt 1]}{0.15ex}} \ce{A <--> B} – Sebastiano Mar 30 '19 at 23:19
  • 1
    @Sebastiano That's for changing the shape of the arrow tips. – egreg Mar 30 '19 at 23:20
  • I thought that it was the key of the solution. – Sebastiano Mar 30 '19 at 23:21
  • This has no effect for me - if I run your code, all the arrows come out the same, long, length. – Nathaniel Feb 8 at 8:08
  • @Nathaniel I don't know what to say: I tried on a fresh document with everything updated and it works as advertised. – egreg Feb 8 at 9:16

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