Activation energy, E_a, (upper panel) and the enthalpy change, ΔH, (lower panel) of type 2, 3, and 4 reactions selected in each step. The red dashed line shows the critical activation energy (E_a,crit = 44 kJ mol⁻¹) under the fiducial timescale and temperature. The orange dashed line shows the threshold (ΔH = −100 km mol⁻¹) which gives E_a,crit = 0 under α = 1.0 and β = 100 kJ mol⁻¹ (see Sect. 2.4.2). For visual convenience, we arbitrarily selected the number of plotting data and randomly shifted the points vertically and horizontally with the small amplitude. The magenta dots are results with E_acrit = 44 kJ mol⁻¹ and the light blue dots are results from the same initial conditions but without limiting E_acrit. They show that the activation energy of the selected reaction is limited by the E_acrit setting. We note that in most steps the light blue dots are hidden by the magenta dots.