## Signs on energy changes

Moderators: Chem_Mod, Chem_Admin

Michelle Steinberg2J
Posts: 73
Joined: Fri Sep 29, 2017 7:04 am

### Signs on energy changes

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
Posts: 51
Joined: Fri Sep 29, 2017 7:07 am
Been upvoted: 1 time

### Re: Signs on energy changes

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 $\bigtriangleup U=q+w$ but it is rearranged into $w=\bigtriangleup U-q$ to solve for work. So it is not exactly "negative".

804899546
Posts: 51
Joined: Sat Jul 22, 2017 3:00 am

### Re: Signs on energy changes

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

Jessica Jones 2B
Posts: 80
Joined: Fri Sep 29, 2017 7:04 am

### Re: Signs on energy changes

yes it would be endothermic!

Return to “Phase Changes & Related Calculations”

### Who is online

Users browsing this forum: No registered users and 2 guests