Step 2: Write what you have underneath the equation.
CH4(g) + 4S(g) --> CS2(g) + 2H2S(g)
m = 35.8 g m = 75.5 g m = ?
Step 3: Convert mass into moles.
mol CH4 = 35.5 g / 16.05 g/mol = 2.21 mol
mol S = 75.5 g / 32.06 g/mol = 2.35 mol
Step 4: Find out what the limiting reagent is. The equation says that for every 4 mol of S you only need 1/4 of that of CH4. So 2.35 x 1/4 = 0.588 mol of CH4 You have 2.21 mol. So the S is the limiting reagent. So all 2.35 mol of S will be used up but will only consume 0.588 mol of the CH4. You should have 2.21 - 0.588 or 1.62 mol of unburned CH4
Step 5: Now compare mol ratios between S and H2S. The ration is 4 to 2 or 2 to 1. So for every mol of S burned you will get 1/2 as many mols of H2S
So 2.21 x 1/2 = 1.105 mol of H2S formed.
Step 6. Convert moles back to mass
mass = 1.105 mol x 34.08 g/mol = 37.7 g
OK?