I think the confusion arises due to difference in equations from Physics and Chemistry text books.
The physics text writes ∆U=q-w while chemistry says ∆U=q+w.
From the physics text its mentioned that work done by the system is positive means ∆U=q-(+w)
and work done on the system is negative means ∆U=q-(-w).
THEREFORE, both are correct in their own way. Hope I've figured it out correctly.
