Determine the theoretical yield of H2S (in moles) if 4.0 mol Al2S3 and 4.0 mol H2O are reacted according to the following balanced reaction. A possibly useful molar mass is Al2S3 = 150.17.I am having a little trouble with this one.nswers. Best Answer: You need 6 moles of H2O for every mole of Al2S3 but you have equal moles so the limiting factor with be the amount of H2O. From the equation 6 moles H2O gives 3 moles H2S So 4 moles H2O will give 2 moles H2S.