Calculate $\Delta H^\circ$ for the following equilibrium processes.
(d) \begin{tikzpicture}[scale=0.8]
\draw (0,0) -- (1,0.5) -- (2,0) -- (3,0.5) -- (3.5,0) -- (4,0.5) -- (4.5,0) -- (4.5,0);
\draw (2.5,0.75) node {$CH_3$};
\draw (4.5,0) -- (5,0);
\draw[<->,double distance=2pt] (4.75,0) -- (5.25,0);
\draw (5.5,0) -- (6.5,0.5) -- (7.5,0) -- (8.5,0.5) -- (9,0) -- (9.5,0.5) -- (10,0);
\draw (9.75,0.75) node {$CH_3$};
\end{tikzpicture}