work done by system or on system

[JacobHershenhouse3G]

I know that deltaU= q + w but how do you differentiate if work and temperature is applied to or by the system from the surroundings? I seem to keep messing up signs and would like some clarification.

[ChathuriGunasekera1D]

Hi! Here is a basic set of guidelines
q is positive if system absorbs energy
q is negative if system releases energy
w is positive if work is being done on the system
w is negative if work is being done by the system

An example is going from solid to liquid; it requires heat to break the IMFs, so the q is positive because energy is absorbed. Because work is being done by the system, w is negative.

[JiangJC Dis2K]

if q for the system is positive, then it absorbs heat. if q is negative, it releases heat and heat is therefore lost to the surroundings. if w is positive for the system, work is done on the system by the surroundings. if w is negative, work is done by the system on the surroundings. hope this helps!

[Vicky Lu 1L]

q (heat) is positive when its has key words such as absorbed/gain energy and is negative when it released/emitted/loses energy. w (work) is positive when work is done on the system and negative when the system does or is doing the work.