The Jander model has been widely applied to the analysis of solid-solid reaction rates. However, it contains some problems which contradict Jander's own experimental work. In this paper, the main problem, i. e, the variation of the rate constant with the molar ratio is explained by the number of contact points between different kind of particles. Furthermore, various mistakes are also pointed out in the so-far published reaction models, anticipating that a new reaction model be proposed by introducing the correct number of contact points.