This study investigates the impact of diffusion-thermo coupling on the transient natural convection of a chemically reactive viscous fluid. The fluid experiences internal heat generation or absorption while flowing through an infinite vertical tube that is subjected to both ramped wall heating and concentration conditions. To analyze this system, the governing transport equations have been transformed using the Laplace technique and solved analytically, expressing the solutions in terms of modified Bessel functions. These equations were then numerically inverted using a Riemann sum approximation to handle the complexities associated with exact inversion. The results are presented for representative fluid properties and system parameters, highlighting the evolution of velocity, temperature, concentration, and associated transfer rates such as Nusselt and Sherwood numbers, as well as skin friction. In addition, steady-state solutions have been derived in closed form, and their convergence with the transient solutions at large time scales has been confirmed. These findings provide valuable insights into the thermofluidic behavior relevant to advanced thermal management, energy systems, and chemically reactive transport processes, particularly where ramped boundary heating plays a crucial role