Considerable effort has been exerted using theoretical calculations to determine solid surface energies. Nanomaterials with high surface energy depending on morphology and size exhibit enhanced reactivity. Thus, investigating the effects of morphology, size, and nanostructure on the surface energies and kinetics of nanomaterials is important. This study determined the surface energies of silver phosphate (Ag3PO4) micro-/nanocrystals and their kinetic parameters when reacting with HNO3 by using microcalorimetry. This study also discussed rationally combined thermochemical cycle, transition state theory, basic theory of chemical thermodynamics with thermokinetic principle, morphology dependence of reaction kinetics, and surface thermodynamic properties. Results show that the molar surface enthalpy, molar surface entropy, molar surface Gibbs free energy, and molar surface energy of cubic Ag3PO4 micro-/nanocrystals are larger than those of rhombic dodecahedral Ag3PO4 micro-/nanocrystals. Compared with rhombic dodecahedral Ag3PO4, cubic Ag3PO4 with high surface energy exhibits higher reaction rate and lower activation energy, activation Gibbs free energy, activation enthalpy, and activation entropy. These results indicate that cubic Ag3PO4 micro-/nanocrystals can overcome small energy barrier faster than rhombic dodecahedral Ag3PO4 micro-/nanocrystals and thus require lower activation energy.