Oxygen dissolves into and reacts irreversibly with aqueous sodium sulphite solutions contained in a vertical container of height H. If the gas solubility is denoted as Cao at the liquid-gas interface, derive the physicochemical model to describe the unsteady-state composition profiles of oxygen in the liquid phase when the rate of oxygen reaction is represented by RA = -kCA and the local oxygen diffusion flux is described by JA =-DOCA, where D is diffusivity and Z is distance from the D z dz interface into the liquid. Also define the appropriate initial and boundary conditions for the system