Chelsea took the lead with the help of Rahem Sterling 1-0 for the first half. with a temporary aggregate of 1-1 and we will soon witness the second half which will begin soon. Chelsea can use the second half to double their lead and this should be their main focus. The game in the first half looked quite interesting where Chelsea were able to make 11 shots. This is a pretty good performance by Chelsea in the Champions League.
Now, Chelsea already leads with 2 goals, the aggregate 2-1 for Chelsea. 
I am surprised that Chelsea played well so far, they seem to be more motivated to qualify for the next stage in UCL. They dominate the match and they become very offensive. If they can keep this good game, no doubt Chelsea to play in the next round. They are playing at home now, they have a bigger chance to qualify.
By the way, Chelsea already made 12 shot attempts, 4 shots on target. While Dortmund only made 5 shot attempts, only 1 shot on target. It is very clear that Chelsea is more superior in this match.