The whole purpose of the reaction environment is to have independent numbering for displayed reactions. If you want the same numbering for displayed reactions and equations you can simply use
\begin{equation}
\ch{ A + B -> C + D }
\end{equation}
Under the hood this is what the reaction environment does after all.
\documentclass{scrartcl}
\usepackage{chemmacros}
\begin{document}
\begin{equation}
\ch{ A + B -> C + D }
\end{equation}
\begin{equation}
\ch{ A + B -> C + D }
\end{equation}
\begin{equation}
1 + 3 = 4
\end{equation}
\end{document}

If you want to use a reaction environment the easiest solution would be to redefine it to just do the above (the following example contains code to make the example works with older and newer versions of chemmacros):
\documentclass{scrartcl}
\usepackage{chemmacros,environ}
% in older versions there is no \IfChemCompatibilityT
\providecommand\IfChemCompatibilityT[3]{}
% load the `reactions' module in newer versions:
\IfChemCompatibilityT{>=}{5.0}{
\usechemmodule{reactions}
}
% redefine the environments:
\RenewEnviron{reaction}
{\begin{equation}\expandafter\ch\expandafter{\BODY}\end{equation}}
\RenewEnviron{reaction*}
{\begin{equation*}\expandafter\ch\expandafter{\BODY}\end{equation*}}
\RenewEnviron{reactions}
{\begin{align}\expandafter\ch\expandafter{\BODY}\end{align}}
\RenewEnviron{reactions*}
{\begin{align*}\expandafter\ch\expandafter{\BODY}\end{align*}}
\begin{document}
\begin{reaction}
A + B -> C + D
\end{reaction}
\begin{reactions}
A + B &-> C + D \\
E + F &<=> G
\end{reactions}
\begin{equation}
1 + 3 = 4
\end{equation}
\end{document}
reactionenvironment and use\begin{equation} \ch{A + B -> C + D} \end{equation}. – cgnieder Sep 16 '15 at 10:03reactionenvironment is to have independent numbering. – cgnieder Sep 16 '15 at 10:04reactionenvironment is: anequationwith the contents wrapped in\ch. – cgnieder Sep 16 '15 at 10:29