Math & Science ⇒ Customize arrow

[bstex]

Hi,
I have already this:

Code: Select all

\documentclass[a4paper,11pt]{book} 

\usepackage{tikz}
\usetikzlibrary{arrows.meta}
\usepackage[version=4]{mhchem}

\begin{document}
\mhchemoptions{arrows=pgf{Straight Barb[left]}{0.12ex}}
\ce{A + B <--> C + D}
\end{document}

which is this:

Screen Shot 2017-11-04 at 17.50.44.png (12.85 KiB) Viewed 4538 times

and I'd like to change the distance between two arrows and the total length of the arrows.
Is it possible?

[Stefan Kottwitz]

First idea for changing the length: add white space as an option in square brackets to the arrow:

\ce{A + B <-->[\hspace{30pt}] C + D}

Stefan

[bstex]

Thank you for your reply, Stefan.
Well, I forgot to mention that I'd like the arrow to be shorter, not longer.