Dominant hydrogen dissociation reactions during annealing of hydrogenated amorphous-silicon nitride were determined by comparison of the bond density dynamics with various reaction models. The sample material was produced with remote plasma-enhanced chemical-vapor deposition, deposited at high-ammonia-to-silane flow ratios (ammonia rich). The heat treatment was performed with rapid thermal annealing at various annealing temperatures and times as well as samples containing different stoichiometries and isotopes (hydrogenated and deuterated). The experiments showed that hydrogen loss during annealing is mostly due to molecular hydrogen (H-2) release as long as SiH bonds are contained in the film. After their exhaustion, an ammonia (NH3) producing reaction prevails at temperatures between 600 and 900 degreesC.