In this work, an investigation of the enthalpy effects on the thermochemical non-equilibrium in hypersonic nozzles is performed. Three different nozzles, with different geometries and stagnation enthalpy conditions are used in this study. The three cases, two of them with stagnation enthalpy conditions of 3.3 MJ/kg and 7.56 MJ/kg, use molecular nitrogen as the testing fluid and in the third case, corresponding to the higher enthalpy condition of 23.8 MJ/kg, the fluid is partially dissociated air composed by five neutral species (N2, O2, NO, N and O). A reliable numerical model, previously validated by the authors, using non-equilibrium Navier-Stokes-Fourier equations within a density-based algorithm is here employed in the OpenFOAM framework. After an estimation of the discretization uncertainties by using the Richardson extrapolation method and Roache’s Grid Convergence Index, the results are obtained by using a sufficient independent grid for each case. It was found that the nozzle with the higher non-equilibrium impact on the flow properties, was the one with the higher expansion ratio, with the difference between equilibrium and non-equilibrium of 17% for the Mach number, 35% for the static pressure and 38% for the static temperature. Using three different stagnation conditions, of 4.92 MJ/kg, 5.98 MJ/kg, and 7.56 MJ/kg, for that nozzle, it was revealed that the increasing of the stagnation enthalpy at the reservoir leads to an increment of the degree of non-equilibrium inside the nozzle, reaching its maximum at the nozzle exit. Increasing the stagnation enthalpy in 1.58 MJ/kg leads to an increment of the non-equilibrium degree in 3.4% for the Mach number, 5.5% for the static pressure and 6.6% for the static temperature.