The decomposition of ammonia at CVD conditions was investigated by kinetic simulations, and it was found that at CVD and ALD like conditions the decomposition of ammonia is limited by kinetics, not reaching equilibrium compositions during the expected residence time for gases in the reactors. This shows that an equilibrium model with almost full decomposition to dinitrogen and dihydrogen cannot be used alone to explain the low reactivity of ammonia in the growth processes. Instead the low reactivity is explained by the low concentration of the more reactive intermediates, e.g. NH2 radicals, that could contribute to film growth. The simulations also show that hydrogen has a passivating effect on decomposition, mainly by reacting with the formed NH2 radicals reforming ammonia before further reactions could occur. Lowering the amount of hydrogen in the carrier has the potential to increase the decomposition rate of ammonia to levels more suited for film deposition.