# How to include a chemical reaction in the equation numbering?

I would like to have my chemical reaction as equation number 0.1 and the equation (K_D) as an equation with the second number 0.2.

  \documentclass[12pt]{article}
\usepackage{amsmath}
\usepackage{chemmacros}

\begin{document}

\begin{align*}
\ch{S + E <>[ $k_{\mathrm{SI}}$ ][ $k_{\mathrm{IS}}$ ] E.I <>[ $k_{\mathrm{PI}}$ ][ $k_{\mathrm{IP}}$ ] P + E}
\begin{align*}

$$\label{} K_{D} = \frac{[A][B]^{N_{max}}}{[AB_{N_{max}]}} = \frac{k_{off}}{k_{on}}.$$

\end{document}


With Alex's suggestion I got this:

This is the SOLUTION:

$$\ch{ A + B -> C + D }$$

• Thanks for providing code with your question. However, at present it does not compile. For completeness and later reference, could you add the \documentclass and the \usepackages? Commented Oct 26, 2017 at 21:12

## 1 Answer

You can use numberwithin{equation}{section}:

    \documentclass[12pt]{article}
\usepackage{amsmath}
\usepackage{chemmacros}
\begin{document}

\numberwithin{equation}{section}
\begin{align}
\ch{S + E <>[ $k_{\mathrm{SI}}$ ][ $k_{\mathrm{IS}}$ ] E.I <>[                 $k_{\mathrm{PI}}$ ][ $k_{\mathrm{IP}}$ ] P + E}
\end{align}

$$\label{} K_{D} = \frac{[A][B]^{N_{max}}}{[AB_{N_{max}]}} = \frac{k_{off}} {k_{on}}.$$

\end{document}

• @Marijn, I added the document class and the packages required to compile.
– Alex
Commented Oct 29, 2017 at 10:57
• unfortunately your solution only provides the numbering expansion of the existing equation numbering Commented Oct 29, 2017 at 16:45
• indeed your example works, but when I transpose it to my case then its not working. See image posted in the question Commented Oct 29, 2017 at 16:51
• solution posted in main question window Commented Oct 29, 2017 at 17:00
• @Mathy, are you adding any \section or \subsection? I don't see a reason to have 0.2.1 instead of 0.1. And why is your first equation without number? Did you see that (in my answer) I removed the asterisks from the align environment?
– Alex
Commented Oct 29, 2017 at 21:35