Assuming it's all on one ticket with airberlin your bags should be checked through.

TXL is a quirky little airport with a strange lay-out.

If you're really lucky you will be bussed to Terminal C after your ORD lands and that will be the terminal from which your KRK departs.

However you are more likely to end up in A or D and then have to make the walk over to C, re-clear security and go to your gate. It's not terribly far, just follow the signs...

Shouldn't be a problem at all on a 1h40 planned layover!