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### Qsystem = -Qsurroundings help

Posted: Sat Jan 16, 2016 11:04 pm
In the equation Qsystem = -Qsurroundings, is the (-) sign only there to account for the idea of work being done vs by a system?

### Re: Qsystem = -Qsurroundings help

Posted: Sun Jan 17, 2016 12:28 am
Inadvertently, yes. The negative sign basically shows that whatever work a system performs is absorbed by its surroundings. Contrarily, whatever work is performed on the system by the surroundings is absorbed by the system and lost by the surroundings. They are equal and opposite.

Hope that helped!

### Re: Qsystem = -Qsurroundings help

Posted: Sun Jan 17, 2016 11:22 am
Adding on to the previous response, the reason why they are equal and opposite is that there is no other energy transfers taking place besides between the system and its immediate surroundings. We assume that there is constant pressure and volume, so in a perfect system, with nothing else acting on it besides the temperature increase/decrease, all of the heat gained is gained directly from its surroundings. So the surroundings lose that same amount of heat, or vice versa.