In a chemical reaction, both material conversions and energy partitioning take place simultaneously. Then its mechanism must be characterized from the viewpoints on both sides. Energy partitioning in surface reactions can be examined on product desorption processes when these are repulsive. This principle is exemplified in CO(a)+O(a) → CO2(g) on Pd(110)(1×1), and its application is proposed for N2O(a) → N2(g)+O(a) on the same surface. Structural information of desorption sites and active intermediates, as well as transition states, can be delivered from desorption-and azimuth-angle dependences of physical quantities of desorbing hyper-thermal products; i.e., anisotropic distributions of their flux, and translational and internal energies.