Kinetics and heat transfer in a CO2/CO/O2/O/C mixture in a hypersonic boundary layer is studied using a state-to-state vibrational-chemical kinetic model. The CO2 molecule is detailed in its symmetric stretching, bending and asymmetric stretching modes, which are strongly coupled through inter-mode vibrational energy transfers. Two sets of rate coeficients for the vibrational energy transitions are used. Different kinetic schemes including various physical and chemical processes are assessed. The heat flux is calculated, in the framework of the modified Chapman-Enskog theory, accounting for the vibrational states of involved molecules. Comparisons with results obtained using a simplified model, including mainly vibrational levels of the asymmetric stretching mode, are carried out. It is shown that VT transitions in the symmetric and asymmetric modes do not alter the flow and can be neglected. The heat flux is not sensitive to the rates of vibrational energy transitions but depends noticeably on the processes implemented to the kinetic scheme. Using the simplified model yields under-predicted surface heat fluxes; nevertheless we can recommend it for fast estimates of the fluid dynamic variables and heat transfer in hypersonic flows since its implementation essentially reduces computational costs.