Chemical reactions in Tex

Test that you have the packages loaded; from the command prompt enter

texdoc chemmacros

...to open The Chemmacros Bundle guide "chemforumla_en.pdf", inspired and based on usefully extending mhchem. 

My example...

\documentclass{article}
\usepackage{chammacros}
\begin{document}
\ch{Na2SO4 ->[ H2O ] Na+ + SO4^2-}\\
\ch{( 2 Na+ ,SO4^2- ) + (Ba^2+ , 2 Cl- ) -> BaSO4 v + 2 NaCl}\\
\ch{2 CaCO3 <=>[ H2O ] 2 Ca^2+ + 2 CO3^2-}\\
\ch{HCOOH + H2O <=>[ H2O ] H3O^+ + HCOO^-}\\
\ch{2 CO3^2-\ + 4H^+ <=> 2 CO2 + 2 H2O} \\
\end{document}