q and w

[Lauryn Jordan 1F]

can someone clarify what q and w are as well as how can you tell if they will be positive or negative?

[Shawn Patel 1I]

Hey,
W is work and Q is heat. Work is motion against an opposing force, and heat is the energy transferred as a result of a temperature difference. When work is done on a system, w is positive, and when work is done by the system, w is negative. If heat enters the system, q is positive, and if heat leaves the system, q is negative.

[Lauryn Jordan 1F]

soooo my follow up question would be when do you know when work is done on a system vs done by a system?

[Kristin Ishaya 1A]

As defined by the textbook, “q is the energy supplied to the system as heat and w is the energy supplied the system as work” (page 278). Basically, q refers to the energy that is transferred or absorbed in a system and work is caused by either an internal or external force that is applied to the system.

[Anh Nguyen 2A]

q is the energy transferred by heat.
w is the energy transferred by doing work.
If heat has flowed from the system then q is negative. If the system absorbs heat then q is positive.
And for w, if work is done on the system then w is positive, like compressing gas inside an insulated container increases its internal energy. If work is done by the system then w is negative (gas expansion).

[Jonathan Tangonan 1E]

Overall, q and w added together make up the internal energy that happens within a system. Q is the energy transferred as heat where a positive q would indicate an absorption of heat while a negative q would indicate a release of heat from the system. A positive w would indicate that work has been done on a system whereas work done by a system would result in a negative w.