  Enhancing chemical reactions, such as $A+B \to [\textit{activated
complex}]^\# \to C+D$, in gas phase through its coupling to
quantum-electrodynamics (QED) modes in a dark cavity is investigated. The main
result is that the enhancement of the reaction rate by a dark cavity is for
asymmetric reactions (products different from reactants.) Notice that in
addition to the cavity been dark, the reactants are in their ground electronic
and vibrational states, i.e., it is indeed dark. Theoretical derivation,
utilizing the non-Hermitian formalism of quantum mechanics (NHQM), provides
conditions and guidelines for selecting the proper type of reactions that can
be enhanced by a dark cavity. Nevertheless, the time-dependent simulations of
such experiments can be carried out using the standard (Hermitian) scattering
theory (but including the conditions derived via NHQM). We believe that this
work opens a gate to new types of studies and hopefully helps to close the gap
between theory and experiments in this fascinating, relatively new field of
research. As an example, we demonstrate that the asymmetric reaction rates of
$O+D_2\to [ODD]^{\#} \to OD+D$ and $H+ArCl \to [ArHCl]^{\#} \to H+Ar+Cl$ can be
enhanced by a dark cavity. Contrary, the dark cavity effect on the symmetric
reaction of hydrogen exchange in methane will be negligible.
