How to make the equilibrium double arrow longer?

Question

\documentclass{article}

\usepackage{mhchem}

\begin{document}  

\ce{H^+ (\textit{aq}) + HCO3^- <=> H2CO3 (\textit{aq}) <=> H2O (\textit{l}) + CO2 (\textit{g})}

\ce{2H2(\textit{g}) + O2(\textit{g}) <=> 2H2O(\textit{l})}

\end{document}

I am new to Latex and doing some chemistry reports and while MS equation editor is a pain, it decently works even by using mixed fractions to get ion charges with subscripts for atoms, but I digress. I cannot do the double harpoon-like symbol for chemical equilibrium "longer" as I like the arrows to be stretched out more than it is. Is this even possible?

Answer 1

Your original version didn't work for me, hence \expandafter's:

\documentclass{article}

\usepackage{mhchem}

\begin{document}

%\ce{H^+ (\textit{aq}) + HCO3^- <=> H2CO3 (\textit{aq}) <=> H2O (\textit{l}) + CO2 (\textit{g})}

\ce{2H2( \expandafter\textit{g}) + O2( \expandafter\textit{g}) <=> 2H2O( \expandafter\textit{l})}

\ce{2H2( \expandafter\textit{ g}) + O2( \expandafter\textit{g}) <=>[\hspace{1cm}][] 2H2O( \expandafter\textit{l})}


\end{document}

Answer 2

First of all, please use mhchem with the version option. You should always read the warnings you get.

Second, why do you try to get the state in italic text? IUPAC recommendation is just normal roman (= upright) text.

You can make the arrows longer by writing some 'space' above them, e.g. \hspace{10ex}.

Are you looking for an option to make all arrows longer by the same value? That is not yet an option available for users, but I could put it on my todo list.

\documentclass{article}
\usepackage[version=3]{mhchem}
\begin{document}  
\ce{H^+(aq) + HCO3^- <=>[\hspace{10ex}] H2CO3(aq) <=> H2O(l) + CO2(g)}

\ce{2H2(g) + O2(g) <=> 2H2O(l)}
\end{document}

Answer 3

Is this what you require?

Then use the following:

\documentclass[12pt]{article}  
\begin{document}  
\begin{eqnarray*}  
H^+ (aq) + HCO3^- &\Longleftrightarrow& H2CO3 (aq) \Longleftrightarrow     H2O (l) + CO2 (g)\\
2H2(g) + O2(g) &\Longleftrightarrow& 2H2O(l)
\end{eqnarray*}
\end{document}