Text Formatting ⇒ mhchem | Trouble with new Command

[ghostanime2001]

I cannot use my new defined command \ces inside \ce{} I get an error. However i can use my defined command outside the array environment but not inside it. What am I doing wrong with this new command? If it can work outside the array environment why isn't it working inside a math environment like array ? I have my command definition enclosed in $ $.

MWE:

Code: Select all

\documentclass[fleqn]{article} 
\usepackage[version=3]{mhchem}
\usepackage{cancel}

\newcommand{\ces}[2]{$\cancel{\ce{#1}}\ce{_{(#2)}}$}

\begin{document}
$\begin{array}[t]{l}
\ce{H2O + \ces{O2}{g} -> H2O + Cl2}
\end{array}$ \\ \\
\ces{O2}{g} 
\end{document}

[cgnieder]

Using commands inside \ce can be a pain. "Hiding" it between $...$ should work:

Code: Select all

\documentclass[fleqn]{article}
\usepackage[version=3]{mhchem}
\usepackage{cancel}

\newcommand{\ces}[2]{$\cancel{\ce{#1}}\ce{_{(#2)}}$}

\begin{document}
$\begin{array}[t]{l}
\ce{H2O + $\ces{O2}{g}$ -> H2O + Cl2}
\end{array}$ \\ \\
\ces{O2}{g}
\end{document}

[ghostanime2001]

It works if you lose the $ $ in the preamble \newcommand definition. This is so strange! it works with the $ $ surrounding the \ces command but not inside the command definition itself since you would expect everything inside the $ $ to be "mathematicized"