Final answer:
The limiting reactant in the reaction of sulfur with oxygen to produce sulfur trioxide gas is sulfur.
Step-by-step explanation:
In order to determine the limiting reactant, we need to compare the amount of product that can be formed from each reactant. First, we need to calculate the number of moles of sulfur and oxygen. The molar mass of sulfur is 32.06 g/mol, so 6.3 g of sulfur is equal to 6.3 g / 32.06 g/mol = 0.196 mol. The molar mass of oxygen is 16.00 g/mol, so 10.0 g of oxygen is equal to 10.0 g / 16.00 g/mol = 0.625 mol.
According to the balanced chemical equation, the ratio of sulfur to oxygen is 1:1. Therefore, the reactant with the lesser amount of moles is the limiting reactant. In this case, sulfur has fewer moles (0.196 mol) compared to oxygen (0.625 mol), so sulfur is the limiting reactant.