Is the second half of a root canal painful?

No: I assume your root canal is being done in two visits. The first visit consists of removing the nerve and cleaning and shaping the canals. The second visit is filling and sealing the canals. Fret not! nowadays, microscopic endodontists often complete the entire procedure in one visit!

Less: Typically the first part if a root canal involves removing a partially live nerve or cleaning out the area on the pulp chamber that contained the nerve. Good anesthetic should make this comfortable. The second part of a root canal is sealing the canals of a dead clean tooth. Should be less than the first.

No: With proper local anesthesia this visit usually is shorter and easier than the first visit . I've even had patients fall asleep!

Root canal: The second half of the root canal should be the same or better than the first appointment if needed. I am assuming your dentist placed some medicine in the canals during the first appointment (the medicine is likely calcium hydroxide). This usually helps to kills bacteria and calm the tooth/tissue down before you second appointment.

Very comfortable: With modern techniques and great anesthetics, most patients report that they are very comfortable during the procedure.