LaTeX problem: The \rightleftarrows symbol is too short

Question

The \rightleftarrows symbol is too short horizontally for my liking. My search engine finds no helpful results for "latex longrightleftarrows". Is there some way to extend the symbol horizontally?

\documentclass[12pt,letterpaper]{article}
\usepackage[utopia]{mathdesign}
\usepackage{amsmath}
\usepackage{mhchem}
\usepackage{gensymb}
 ...
\begin{document}
\ce{\rightleftarrows}
\end{document}

Answer 1

If you are happy with harpoons, you can use xleftrightharpoons from mathtools

\documentclass[12pt,letterpaper]{article}
\usepackage[utopia]{mathdesign}
\usepackage{mathtools}
\usepackage{mhchem}
\usepackage{gensymb}

\begin{document}

\ce{A\rightleftarrows B}

\ce{A\xleftrightharpoons{\rule{2cm}{0pt}} B}

\ce{A\xleftrightharpoons{\hphantom{\hspace*{1cm}}} B}


\end{document}

\documentclass[12pt,letterpaper]{article}
\usepackage[utopia]{mathdesign}
\usepackage{mathtools}
\usepackage{mhchem}
\usepackage{gensymb}

\begin{document}

\ce{A\rightleftarrows B}

\ce{A\xleftrightharpoons{\text{my reaction}} B}



\end{document}

Another variant:

\documentclass[12pt,letterpaper]{article}
\usepackage[utopia]{mathdesign}
\usepackage{mathtools}
\usepackage{mhchem}
\usepackage{gensymb}
\newcommand{\myrightleftarrows}[1]{\mathrel{\substack{\xrightarrow{#1} \\[-.9ex] \xleftarrow{#1}}}}

\begin{document}

\ce{A\rightleftarrows B}

\ce{A\myrightleftarrows{\rule{2cm}{0cm}} B}    %%% change 2cm as you wish
\end{document}

Answer 2

If you are willing to use chemfig you can easily control the arrow attributes:

\documentclass[12pt,letterpaper]{article}
\usepackage[utopia]{mathdesign}
\usepackage{amsmath}
\usepackage{mhchem}
\usepackage{gensymb}
 \usepackage{chemfig}

\begin{document}

\ce{A\rightleftarrows B}

\schemestart
A\arrow{<=>}B 
\schemestop

\setarrowdefault{0,0.7,red,thick}
\schemestart
A\arrow{<=>}B 
\schemestop

\end{document}