Signs on energy changes

[Michelle Steinberg2J]

I am having difficulty with determining the correct signs on energy changes. For example, HW problem 5, why is compression a positive value? Also, HW problem 7 says the system "absorbed 492 J of heat." Why is this a negative value?

Thanks!

[Hammad Khan 2B]

In problem 5,the compression is a positive value because work is being DONE TO the system meaning that energy is being added to it in the form of work. In problem 7, when it says "absorbed heat" it's saying how heat is essentially being taken into a system as it's increasing in energy. The equation is usually written as but it is rearranged into to solve for work. So it is not exactly "negative".

[804899546]

So in number 7, would it be endothermic because it is absorbing heat?

[Jessica Jones 2B]

yes it would be endothermic!