  Interactions between exoplanetary atmospheres and internal properties have
long been hypothesized to be drivers of the inflation mechanisms of gaseous
planets and apparent atmospheric chemical disequilibrium conditions. However,
transmission spectra of exoplanets has been limited in its ability to
observational confirm these theories due to the limited wavelength coverage of
HST and inferences of single molecules, mostly H$_2$O. In this work, we present
the panchromatic transmission spectrum of the approximately 750 K, low-density,
Neptune-sized exoplanet WASP-107b using a combination of HST WFC3, JWST NIRCam
and MIRI. From this spectrum, we detect spectroscopic features due to H$_2$O
(21$\sigma$), CH$_4$ (5$\sigma$), CO (7$\sigma$), CO$_2$ (29$\sigma$), SO$_2$
(9$\sigma$), and NH$_3$ (6$\sigma$). The presence of these molecules enable
constraints on the atmospheric metal enrichment (M/H is 10--18$\times$ Solar),
vertical mixing strength (log$_{10}$K$_{zz}$=8.4--9.0 cm$^2$s$^{-1}$), and
internal temperature ($>$345 K). The high internal temperature is suggestive of
tidally-driven inflation acting upon a Neptune-like internal structure, which
can naturally explain the planet's large radius and low density. These findings
suggest that eccentricity driven tidal heating is a critical process governing
atmospheric chemistry and interior structure inferences for a majority of the
cool ($<$1,000K) super-Earth-to-Saturn mass exoplanet population.
