Use dedicated packages for
- math,
- chemical formulas,
- typesetting of physical quantities.
Don't move the parts in brackets to the right margin.
\documentclass{article}
\usepackage{amsmath}
\usepackage{array}
\usepackage{chemformula}
\usepackage{siunitx}
\begin{document}
\begin{equation*}
\sisetup{per-mode=fraction}
\begin{array}{@{} c @{\hspace{4em}} >{\displaystyle}l @{}}
\ch{CO + 2 H2 <-> CH2OH} & \biggl[\Delta H_0^R = \qty{-90.8}{\kilo\joule\per\mol}\biggr]
\\[3ex]
\ch{CO2 + 3 H2 <-> CH_3OH + H2O} & \biggl[\Delta H_0^R = \qty{-49.6}{\kilo\joule\per\mol}\biggr]
\end{array}
\end{equation*}
\end{document}

If you need to number the equations, you can use IEEEeqnarray
.
\documentclass{article}
\usepackage{amsmath}
\usepackage{array}
\usepackage{chemformula}
\usepackage{siunitx}
\usepackage{IEEEtrantools}
\sisetup{per-mode=fraction}
\begin{document}
\begin{IEEEeqnarray}{c"l}
\ch{CO + 2 H2 <-> CH2OH} & \biggl[\Delta H_0^R = \qty{-90.8}{\kilo\joule\per\mol}\biggr]
\\
\ch{CO2 + 3 H2 <-> CH_3OH + H2O} & \biggl[\Delta H_0^R = \qty{-49.6}{\kilo\joule\per\mol}\biggr]
\end{IEEEeqnarray}
\end{document}
