One thing I think it's interesting to note is that you'll never be able to have that reaction happen in the standard temperature and pressure; you can, however, have the resulting ammonia in the STP.
Anyhow,
Every one mol of nitrogen makes two moles of ammonia, so we have
Since we know that at STP 1 mol of gas has 22.4 L (this can easily be checked by plugging the appropriate values in