Negative sign on work equation

[romina_4C]

Why is there a negative on the w = - P times delta V? Is there any situation where this would not be the case?

[Tai Metzger 3K]

W will be negative if the system is doing work (expansion) and will be positive when work is being done on the system (compression). I hope this helps!

[Veronica_Lubera_2A]

Yes, in expansion there will be a negative sign because the system is losing energy.

[DanielTalebzadehShoushtari2A]

I agree with the above explanations in that the whole term for w is positive/negative depending on whether or not the system is expanding or being compressed. You can think of the negative sign in the formula in a different way: w stands for work being done on the system. In this way, expansion would make delta V positive, and work done on the system is negative (because work is being done by system instead). It works similarly for compression.
In this way, w can be put into the context of U = q + w and make sense because work being done on the system is part of the total energy that the system has.