The rigorously defined criticality condition established by the authors is applied to the Arrhenius model. The dependence of the critical temperature theta* on both the ambient temperature theta(a) and the order of reaction n is demonstrated. All solutions for theta* as a function of theta(a) for any value of n pass through the point of theta(a) = 0.25, theta* = 0.5 (the transition point for n = 0). It is shown that a transition temperature exists for all degrees of reaction except for 0 < n less than or equal to 1.0. For a first order reaction, theta* monotonically increases with the ambient temperature and reaches infinity at theta(a) = 0.5. For 0 < n less than or equal to 1.0, no solution exists for theta* > 1/2(1 - n), no transition temperature exists, and the solution for theta* as a function of theta(a) passes through an inflection point at theta(a) = 0.25, theta* = 0.5. It is also shown that there is significant difference between the results obtained from the Arrhenius model and those from the Frank-Kamenetskii approximated model. The critical state in the theta-tau plane is found to be subcritical in both the theta-Z and the psi-theta* planes. which produce identical results. Proof is provided that criticality in the theta-tau plane coincides with that in the theta-Z and psi-theta* planes only when n = 0 or B = infinity. The criticality limits with different ambient temperature theta(a) for zero order reaction (n = 0) are established. The solution also treats various initial conditions for a zero order reaction.