b) A solution of 500 kg of Na2SO4 in 2500 kg water is cooled from 333 K to 283 K in an agitated mild steel vessel of mass 750 kg. At 283 K, the solubility of the anhydrous salt is 8.9 kg/100 kg water and the stable crystalline phase is Na2SO4.10H20. At 291 K, the heat of the solution is -78.5 MJ/kmol and the specific heat capacities of the solution and mild steel are 3.6 and 0.5 kJ/kg deg K respectively. During cooling, 2 percent of the water initially present is lost by evaporation. Determine the heat which must be removed. Given: The molecular mass of the hydrate = 322 kg/kmol Molecular mass of Na2SO4 = 142 kg/kmol Latent heat of vaporization of water = 2395 kJ/kmol