6 g of O2 gas at STP is expanded so that volume is doubled. Thus, work done is

Expansion work, W=−pext ΔV=−ext Vfinal −Vintial pext =1atmVinital = volume of 6g=13molO2 at STP=5.6LVfinal =11.2L Thus, ΔV=5.6LW=−(1atm×5.6L)=−5.6L atm