U = q +w or U = q-w??

[HaoYun_Liew_1I]

I see both formulas occasionally show up in different formulas, and it is the variable w that seems to be confusing since sometimes +w represents working being done by the system (expansion) vs +w being work done on the system (compression), and im not sure in which formula where +w is work is done by the system and vice versa?

[Brian Bognuda 2I]

The correct equation is U = q + w. An easy way to remember this is when a reaction is isothermal, U = 0, which makes q = -w. Hope this helps.

[Callista OConnor]

It is always q + w. Your confusion may be coming from the fact that sometimes, when delta U = 0, we set w = -q to get a work equation that utilizes the reversible heat equation (with a negative sign in front).

[105561735]

The way I remember it is that U=q+ w and delta u= -W