Number mhchem reactions and create a \listofreactions

Using the chemmacros package:

\documentclass{article}
\usepackage{chemmacros}
\chemsetup{
  modules = {reactions} ,
  formula = mhchem
}
\begin{document}

\listofreactions

\begin{reaction}[bla]
 $A$ ->[H2O] $B$
\end{reaction}

\begin{reaction}
 SO4^2- + Ba^2+ -> BaSO4 v
\end{reaction}

\end{document}

To develop an environment \begin{reaction}...\end{reaction} you can use the code below:

\documentclass{article}
\usepackage{amsmath,mhchem}
\newenvironment{reaction}{\begin{equation}}{\end{equation}}
\newenvironment{reaction*}{\begin{equation*}}{\end{equation*}}
\begin{document}
\begin{reaction}
 \ce{$A$ ->[\ce{+H2O}] $B$}
\end{reaction}
\begin{reaction}
\ce{SO4^2- + Ba^2+ -> BaSO4 v}
 \end{reaction}
\end{document}

To develop a listofreactions use the titletoc package.

This is my solution now including a separate reaction counter and a new list of reactions. It is not fully tested yet but works in my simple test document

\documentclass{article}
\usepackage{amsmath,mhchem}
\usepackage{tocloft}
\newcommand{\reactionlistname}{List of reactions}
\newlistof{reactions}{rxs}{\reactionlistname}

\newcounter{reaction}
\newcounter{tmp}
\newenvironment{reaction}[1][\relax]{%
\setcounter{tmp}{\value{equation}}
\setcounter{equation}{\value{reaction}}
\renewcommand{\theequation}{\arabic{equation}}
\begin{equation}
\addcontentsline{rxs}{reactions}{\protect\numberline{\thereaction}#1}
}{%
\end{equation}
\setcounter{reaction}{\value{equation}}
\setcounter{equation}{\value{tmp}}
}


\begin{document}


\listofreactions

\begin{reaction}[bla]
 \ce{$A$ ->[\ce{+H2O}] $B$}
\end{reaction}

\begin{reaction}
\ce{SO4^2- + Ba^2+ -> BaSO4 v}
 \end{reaction}

\end{document}