Sign convention of heat and work

Sign Conventions for Heat and Work

The signs of 'w' and 'q' are related to the internal energy change. When 'w' or 'q' is positive, it means that energy has been supplied to the system as work or as heat. The internal energy of the system in such a case increases. On the other hand, if 'w' or 'q' is negative, it means that energy has left the system as work or heat. The internal energy of the system decreases. The signs of 'q' and 'w' are:

Heat absorbed by the system= q positive

Heat evolved by the system= q negative

Work done on the system= w positive

Work done by the system= w negative