Here we present an analytical formalism to produce abundances in atmospheres of giant exoplanets under chemical equilibrium. This work consist in 2 parts: The fist part, which is finished and ended with a code (available on Github), simulates the abundance of molecules in a hot atmosphere dominated by hydrogen, which creates graphs similar to those presented in the paper "Carbon dioxide in exoplanetary atmospheres: Rarely dominant compared to carbon monoxide and water in hot atmospheres dominated by hydrogen" by Kevin Heng et al. (2015). The second part, which is still on process, modify the fist part with an implementation of TiO, which is being added to the equations of Heng using the classic work of Lodders (2002) in the subject. We will try to see in this second part what the TiO can tell us about the C/O ratio and how the abundances of TiO are related to those of other oxygen-carrying molecules.