  We present a grid of forward model transmission spectra, adopting an
isothermal temperature-pressure profile, alongside corresponding equilibrium
chemical abundances for 117 observationally significant hot exoplanets
(Equilibrium Temperatures of 547-2710 K). This model grid has been developed
using a 1D radiative-convective-chemical equilibrium model termed ATMO, with
up-to-date high temperature opacities. We present an interpretation of
observations of ten exoplanets, including best fit parameters and $\chi^{2}$
maps. In agreement with previous works, we find a continuum from clear to
hazy/cloudy atmospheres for this sample of hot Jupiters. The data for all the
10 planets are consistent with sub-solar to solar C/O ratio, 0.005 to 10 times
solar metallicity and water rather than a methane dominated infrared spectra.
We then explore the range of simulated atmospheric spectra for different
exoplanets, based on characteristics such as temperature, metallicity,
C/O-ratio, haziness and cloudiness. We find a transition value for the
metallicity between 10 and 50 times solar, which leads to substantial changes
in the transmission spectra. We also find a transition value of C/O ratio, from
water to carbon species dominated infrared spectra, as found by previous works,
revealing a temperature dependence of this transition point ranging from
$\sim$0.56 to $\sim$1-1.3 for equilibrium temperatures from $\sim$900 to
$\sim$2600 K. We highlight the potential of the spectral features of HCN and
C$_2$H$_2$ to constrain the metallicities and C/O ratios of planets, using JWST
observations. Finally, our entire grid ($\sim$460,000 simulations) is publicly
available and can be used directly with the JWST simulator PandExo for planning
observations.

Earth and Planetary Astrophysics