# chemfig - Redox semi-reaction

It is possible write the two redox half-reactions inside a brace, so as to obtain a thing as in this figure? I'm using chemfig package

Here's my small attempt at creating the half equations.

The code:

\documentclass{article}
\usepackage{amsmath}
\usepackage[dvipsnames]{xcolor}
\usepackage{chemmacros}
\begin{document}
\begin{aligned} {\color{OliveGreen} 3} \\ {\color{OliveGreen} 1} \end{aligned}% \left\{% \begin{aligned} &\ch{H2S -> S + 2 \el} \\ &\ch{Cr2O7\mch[2] + 6 \el -> 2 Cr\pch[3]} \end{aligned} \right.
\centerline{\rule{6cm}{1pt}}
${\color{OliveGreen} 8 \color{blue} \ch{H\pch}} + {\color{OliveGreen} 3} \ch{H2S + Cr2O7\mch[2] ->} {\color{OliveGreen} 3} \ch{S + 2 Cr\pch[3] +} {\color{OliveGreen} 7 \color{blue} \ch{H2O}}$
\end{document}


If alignment is not a huge issue for the half equations, then \begin{cases}...\end{cases} is a more succinct answer (Thanks @Moriambar!). In that case (no pun intended), the half equations can be typeset as such:
...
\begin{aligned} {\color{OliveGreen} 3} \\ {\color{OliveGreen} 1} \end{aligned}% \begin{cases} % <------------- NOTE \ch{H2S -> S + 2 \el} \\ \ch{Cr2O7\mch[2] + 6 \el -> 2 Cr\pch[3]} \end{cases}

• Can you use cases? Or is it not suited for this case? – Moriambar Apr 14 '17 at 9:28
• @Moriambar Yup I think so. It's embarrassing, I initially wanted to align the arrows, which is why I used aligned, but later I realised OP's pic is left aligned, so I just shifted the &s without thinking much. I'll add an addendum, thanks for the comment! – Troy Apr 14 '17 at 9:32