"3-way" reaction in LaTeX

Question

I would like to write an equation with three different states, does anyone know how to do this?

Answer 1

The following MWE that uses the chemfig package might serve as a place to start from:

\documentclass{article}
\usepackage{chemfig}
\begin{document}

\schemestart
\chemfig{CO_2} \+ \chemfig{H_2O} \arrow(A--B){<=>[$k_{+2}$][$k_{-2}$]}[,1.5,,] \chemfig{H_2CO_3}
\arrow(@A--C){<=>[${k*_{+1}}$][${k*_{-1}}$]}[-45,1.5,,] \chemfig{HCO_{3}^{-}} \+ \chemfig{H^+}
\arrow(@C--@B){<=>[$k_{+3}$][$k_{-3}$]}[,1.5,,]
\schemestop

\end{document}