If 20 grams of sulfur reacts with 30 grams of oxygen, predict the mass of sulfur trioxide produced. Why would you expect this

20/32=0.625 moles of sulfur

30/16 = 1.875 moles of oxygen

The formula requires 1 mole of sulfur for 3 moles of oxygen which means that their is no limiting reactant as that is the ratio found thus it will react to completion forming 50 grams of product or sulfur trioxide