I doubt that Arsenal can win this round, indeed both teams still have the same chance, but in the next match Arsenal will face Munich away, of course this will make Arsenal feel pressured and I'm not sure that even if Arsenal uses all their strength, Munich will also do the same thing, let alone competing at home will make Munich more confident to win.
Bayern are unstable this season and they lost to outsiders both home and away, so with Arsenal the result could be anything in the return game, playing at the home stadium will not give Bayern significant bonuses. Let's say it will be difficult for Arsenal to win (this is 100%) but they can dry out the game (like in the game with City) and then there is a high probability that we will see extra time and a penalty shootout.
Honestly anything can happen in the second leg between these two teams. The only advantage is that Arsenal is in a really good form and they play really well,while Bayern Munich lost all their titles this year plus are in a really bad form and they only got champions league to try and get a trophy,but with how bad Bayern Munich is playing i dont see them going into the semi-final only by some really big luck.