The clean and environmentally friendly energy demand increases rapidly over the years. Hydrogen has been recognised as one of the best options to satisfy this demand. Utilisation of hydrogen as an energy carrier requires a number of steps especially for on-board applications, namely, production, transportation and storage. Storage of hydrogen brings a great challenge for the researchers among others. Current technologies include high-pressure compression, liquefaction and solid state storage of hydrogen. Solid state storage of hydrogen seems to be more applicable due to being much safer and denser. Metal hydrides are accepted as good candidates for solid state storage of hydrogen. In this regard, this study focuses on revealing dynamical and mechanical properties of new hydrogen reservoirs with high gravimetric hydrogen density, Li-X-H (X = C, N) using first principle calculations. First principle calculations have been proven to be a great tool to reveal extensive physical and chemical properties of the materials as well as mechanical and dynamical stability without synthesising them. Thus, this study adopts this tool to compute several physical and thermodynamic properties of Li-X-H such as bulk modulus, Young Modules, Shear Modulus, elastic constants, Poisson's ratio, Debye Temperature and so on for the first time. Based on the mechanical stability evaluation of compounds using elastic constants, both compounds are found to be mechanically stable. In addition, according to Pugh's criteria, the compounds have ductile nature. The computation of anisotropy revealed that the compounds are anisotropic at all planes. Also, the specific heat capacities of compounds seem to reach to Dulong-Petit limit at high temperatures. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.