I agree with you that Barcelona will win against Napoli in the second leg of the UEFA Champions League Round of 16 matches. Napoli's performance against Barcelona was poor. Napoli just managed to have one shot on target against Barcelona, which led to a goal that earned them a draw. With Napoli's present form, it will be hard for them to beat Barcelona at Camp Nou.
While Barcelona being the favorite during the second leg should not surprise anyone that watched the first leg, at the same time it should be worrying that the only clear opportunity Napoli got ended up in a score, so Barcelona cannot attack recklessly during their upcoming match or Napoli could seriously punish any mistake they make on defense and get a surprising win that no one expected.
Barcelona must not be complacent about the advantage of playing at home, anything can still happen and Napoli will try to play more solidly in order to get a ticket to the quarter-finals. Barcelona back line is still very easy to penetrate, Napoli will exploit this weakness to steal a goal at Camp Nou. In my opinion, the chances of both teams are still 50:50, Barcelona and Napoli still have a chance of qualifying for the next round.
It is very interesting to see these two teams meet in one match, last season they performed well by successfully winning trophies in their respective leagues. However, this season their performance is still very far from expectations.