At STP, 1 mol of gas occupies 22.4 L of volume. Using this conversion we the starting amounts of the reactants: 1.6071 mol H2 .5357 mol CS2 The balanced equation is: 4H2 + CS2 -> CH4 + 2H2S This means that 4 moles of H2 reacts with 1 mole of CS2. Multiplying this ratio with each of the amounts of the reactants: required CS2 based on amount of H2 = 0.4018 mol CS2 required H2 based on amount of CS2 = 2.1428 mol H2 Therefore, the excess reactant is CS2. To calculate how much is left, we simply subtract the amount of the reactant CS2 with the required amount based on the amount of H2: 0.5357 mol - 0.4018 mol = 0.1339 mol
