2 Na + 2 H2O --> 2 NaOH + H2
You place a 31 g piece of sodium metal in excess water at STP. Calculate the volume of hydrogen gas evolved.
mols Na = grams/molar mass = 31/atomic mass Na = ?
Convert mols Na to mols H2 gas. mols H2 x 1/2 = mols H2
Then remember that 1 mol H2 occupies 22.4 L @ STP
Post your work if you get stuck.