The TV is 55 inches, and weighs about 40 pounds. The wall mount I plan on using will be able to reach 2 studs. Will this be enough to support the TV? Does it make a difference if the wall is a load bearing wall or not?
So long as the lags make it into a stud or multiple studs (presuming it is a wood frame house) if the mount is that large, any wall should be fine. Load bearing walls are not needed for mounting a tv They ARE needed for supporting a higher floor(s) and/or roof; that is the load they are bearing.
The keys to successful wall mounting are following directions and ensuring the mount is rated strong enough for your tv.