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### Work

Posted: Mon Feb 04, 2019 1:16 am
How can we determine whether the work is performed by or on the system? What makes work positive or negative in terms of the system?

### Re: Work

Posted: Mon Feb 04, 2019 1:31 am
Work is positive (done on the system) if it adds energy to the system. For example, if you increase the pressure of a gas using a piston, you are doing work on the gas because you are adding energy to it. If you heat a gas, you are adding energy to it, therefore you are doing work on it.

### Re: Work

Posted: Mon Feb 04, 2019 1:38 am
So does that mean work can't be negative?

### Re: Work

Posted: Mon Feb 04, 2019 2:24 am
Work can be negative if it is done by the system, opposite of doing work on the system in that heat is released in contrast to adding heat, or energy.

### Re: Work

Posted: Mon Feb 04, 2019 9:08 am
If work is done on the system it is positive. If work is done by the system it is negative. This is kind of like temperature changes in a system being endothermic and exothermic. If heat is being given into a system it’s positive and if heat is leaving the system it’s negative.

### Re: Work

Posted: Mon Feb 04, 2019 9:43 am
I think of work like exothermic and endothermic. Doing work on a system is positive because you are adding energy. Work by a system is negative because energy is released.

### Re: Work

Posted: Mon Feb 04, 2019 10:00 am
If work is positive, then it is adds energy into the system. If it is negative, energy is released!