w=-P*deltaV

[Janice Xiao 1I]

Can someone explain why there's a negative sign in the w=-P*deltaV equation?

[Jason Liu 1C]

At a constant pressure, if volume increases, it means that the system is expanding and energy is leaving the system as work. This leaves the system with a lower internal energy. The negative sign means that when a system expand, it is losing energy as work.

[Julianna Thrasher 1B]

We use this equation when the system is at equilibrium (and is therefore reversible) in order to calculate work done by expansion against constant pressure and slight changes in volume. The negative sign shows the system is losing energy.

[aTirumalai-1I]

Take a look at this response; it really helped me understand the conceptual reasoning behind it:

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