\documentclass[fleqn,12pt,a4paper]{article} % normal % \documentclass[fleqn,a0,portrait]{a0poster} % poster \usepackage{amsmath,chemarrow} \begin{document} % \tiny % \footnotesize % \small \normalsize % \large % \Large % \LARGE % \huge % \Huge \newcommand{\aqua}{\ensuremath{\text{H}_{\text{2}}\text{O}}} \newcommand{\acid}{\ensuremath{\text{H}_{\text{3}}\text{O}^{\text{+}}}} \newcommand{\base}{\ensuremath{\text{OH}^{\text{$-$}}}} % \section{size check} % % \fbox{{\symbol{65}}} % \fbox{{\symbol{66}}} % \fbox{{\symbol{67}}} % \fbox{{\symbol{68}}} % \fbox{{\symbol{69}}} % \fbox{{\symbol{70}}} % \fbox{{\symbol{71}}} % % {\Huge % \fbox{{\arro\symbol{65}}} % \fbox{{\arro\symbol{66}}} % \fbox{{\arro\symbol{67}}} % \fbox{{\arro\symbol{68}}} % \fbox{{\arro\symbol{69}}} % \fbox{{\arro\symbol{70}}} % \fbox{{\arro\symbol{71}}} % } \section{chemarrow} \begin{displaymath} \aqua + \aqua\ \chemarrow\ \acid + \base \end{displaymath} \section{rarrowfill 2.5em} \begin{displaymath} \aqua + \aqua \rarrowfill{2.5em} \acid + \base \end{displaymath} \section{larrowfill 2.5em} \begin{displaymath} \aqua + \aqua \larrowfill{2.5em} \acid + \base \end{displaymath} \section{rightleftharpoonsfill 2.5em} \begin{displaymath} \aqua + \aqua \rightleftharpoonsfill{2.5em} \acid + \base \end{displaymath} \section{leftrightharpoonsfill 2.5em} \begin{displaymath} \aqua + \aqua \leftrightharpoonsfill{2.5em} \acid + \base \end{displaymath} \section{autorightleftharpoons} \begin{displaymath} \aqua + \aqua \autorightleftharpoons{$k_a$}{$k_b$} \acid + \base \end{displaymath} \section{autoleftrightharpoons} \begin{displaymath} \aqua + \aqua \autoleftrightharpoons{$k_a$}{$k_b$} \acid + \base \end{displaymath} \section{autorightarrow} \begin{displaymath} \aqua + \aqua \autorightarrow{$k_a$}{$k_b$} \acid + \base \end{displaymath} \section{autoleftarrow} \begin{displaymath} \aqua + \aqua \autoleftarrow{$k_a$}{$k_b$} \acid + \base \end{displaymath} \end{document}