The equations that describe partial thermodynamic functions for graphite intercalation compounds (GIC) have been obtained. The derived equations determine the difference of chemical potentials between the intercalant in GIC layers and pure liquid intercalant in the first and the second order of approximation. The notion of T* temperature have been formulated, that determines the boundary of thermal stability of GIG. The formulated physical model of thermoexfoliation process of GIC is in agreement with experimental data.