Hydrogen production by water splitting method is one of the promising solutions for the future energy systems. Among all hydrogen production processes, thermo-chemical Iodine–Sulfur process is one of the efficient and environmentally attractive methods. Iodine–Sulfur process consists of three chemical reactions: (i) Bunsen reaction, which is the acid production step, (ii) sulfuric acid decomposition to produce oxygen and (iii) hydrogen iodide decomposition to produce hydrogen. A detailed parametric study of Bunsen reaction has been carried out through semi-batch experiments. Experiments are carried out in a metallic tubular Bunsen reactor at different pressure and temperature with pure sulfur dioxide (SO2). It has been observed that the overall reaction rate increases with increase in pressure and decreases with increase in temperature. Further studies have been carried out with nitrogen in SO2 to understand the effect of gas film resistance on the overall reaction rate and conversion. © 2015 Hydrogen Energy Publications, LLC.