A system receives 96 J of electrical work, performs 257 J of pressure-volume work, and releases 175 J of heat. What is the change in the internal energy of the system?

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There is no really positive or negative work. However, there is a proper convention so as to prevent confusion with regards to mathematical computation in thermodynamics.

If work is done **on the system** then it has a negative sign.

If work is done **by the system** then it has a positive sign.

OR

Heat is added = positive

Heat is removed = negative

receives 96 J of electrical work = + 96 J

performs 257 J of pressure-volume work = + 257 J

releases 175 J of heat = -175 J

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total = 96 + 257 - 175

**total = 178 J = change in the energy of the system**

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