使用 mhchem 和 TikZ 时无法在流程图中的化学方程式中换行

Question

我似乎无法在方程式中间找到一个换行符；在这个例子中，它无法放入一个框中（并且不会改变框的大小）。我通常的方法 \\不起作用。

\documentclass[12pt]{report}
\usepackage{tikz}
\usepackage[version=3]{mhchem}
\usepackage{amsmath}

\begin{document}
\centering
\begin{figure}

\tikzstyle{1L} = [rectangle, draw, text width=8cm, text centered, fill=blue!20]
\tikzstyle{2L} = [rectangle, draw, text width=5cm, text centered, fill=blue!20]
\tikzstyle{arrow} = [thick,->,>=stealth,-to,shorten >=5pt, shorten <=2pt]

\begin{tikzpicture}[node distance=4cm]


\node (1L) [1L]  {\underline{Oxidation}
    \begin{equation} \ce{ $\underset{\text{Pyrite}}{\cf{FeS2}}$ + 3.5O2 + H2O ->  Fe^2+ + 2SO4+2- + 2H+}
    \end{equation}
};


\node (2L)  [2L,below of=1L, minimum height=3em] {Fe$^{2+}$};


\draw [arrow] (1L)--(2L);

\end{tikzpicture}
\caption{Flowchart}
\end{figure}


\end{document}

Answer 1

你不能在方程中使用\\。这与 TikZ 或mhchem最简单的方法是使用split这里或者在框内用几行写完整个内容：

% arara: pdflatex

\documentclass[12pt]{report}
\usepackage{tikz}
\usepackage[version=3]{mhchem}

\begin{document}    
    \begin{figure}
        \centering      
        \tikzstyle{1L} = [rectangle, draw, text width=8cm, text centered, fill=blue!20]
        \tikzstyle{2L} = [rectangle, draw, text width=5cm, text centered, fill=blue!20]
        \tikzstyle{arrow} = [thick,->,>=stealth,-to,shorten >=5pt, shorten <=2pt]       
        \begin{tikzpicture}[node distance=4cm]  
            \node (1L) [1L]  {\underline{Oxidation}
            \begin{equation}\begin{split} 
                &\ce{ $\underset{\text{Pyrite}}{\cf{FeS2}}$ + 3.5O2 + H2O -> }\\
                &\ce{Fe^2+ + 2SO4+2- + 2H+}
            \end{split}\end{equation}
            };  
            %       
            \node (2L)  [2L,below of=1L, minimum height=3em] {Fe$^{2+}$};   
            %
            \draw [arrow] (1L)--(2L);       
        \end{tikzpicture}
        \caption{Flowchart}
    \end{figure}        
\end{document}