  In the regime of ensemble vibrational strong coupling (VSC), a macroscopic
number $N$ of molecular transitions couple to each resonant cavity mode,
yielding two hybrid light-matter (polariton) modes, and a reservoir of $N-1$
dark states whose chemical dynamics are essentially those of the bare
molecules. This fact is seemingly in opposition to the recently reported
modification of thermally activated ground electronic state reactions under
VSC. Here, we provide a VSC Marcus-Levich-Jortner electron transfer model that
potentially addresses this paradox: while entropy favors the transit through
dark-state channels, the chemical kinetics can be dictated by a few polaritonic
channels with smaller activation energies. The effects of catalytic VSC are
maximal at light-matter resonance, in agreement with experimental observations.
