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A system receives 96 J of electrical work, performs 257 J of pressure-volume work, and...

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spock3 | Student, Undergraduate | (Level 2) Honors

Posted May 7, 2013 at 10:18 AM via web

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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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jerichorayel | College Teacher | (Level 1) Senior Educator

Posted May 24, 2013 at 4:06 PM (Answer #1)

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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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