Create the Equation: How many Liters of SO3 gas (at STP) would be produced from 18.4 g oxygen gas reacted with excess sulfur? *

STP conditions, which are defined as a pressure of 100 kPa and a temperature of 273.15 K, should immediately get you thinking about molar volume of a gas.

More specifically, about the fact that 1 mole of any ideal gas occupies exactly 22.7 L at STP.

This means that all you really need to figure out is the number of moles of oxygen that took part in the reaction. If you know how many moles of oxygen are needed, you can use the molar volume of a gas at STP to calculate the volume of oxygen.

Use water's molar mass to determine how many moles of water would the reaction produce

"the periodic table is arranged in order of atomic number."