Achieve Homework

[Heidi22J]

Can someone please explain number 20 on the achieve homework in simply terms. In general I would like a clear explanation on the relationship between internal energy, work, heat, and systems.

[Truman Ma 3I]

Hi, I assume you mean for Weeks 3-4 hw?

The change in U (ΔU) represents the change in internal energy. Therefore, any arrows moving into the system (whether it be q or w) would represent a positive ΔU value. q (heat) and w (work) are just two different ways to increase or decrease the change in internal energy, but they entail different methods to change internal energy.

q is heat, so this is what solely determines whether the process is endothermic or exothermic.
w is work, so this is energy used to compress (positive w) or to spread out (negative w) the sample in the box.

I'm not sure if we have the same number 20, but more arrows pointing inward means a positive ΔU and more arrows pointing outwards means a negative ΔU.

Hope this helps!

[Ashwin Kumar 3D]

For this problem, the value ΔU represents the change in internal energy. While looking at the images, if there are any arrows moving into the system there would be a positive ΔU value and vice versa. The value q represents heat, so this is what you would use to determine if the process is endothermic or exothermic. The way I approached this questions is that I thought of it as the more arrows that were pointing inward represented a positive ΔU and the more arrows pointing outwards represented a negative ΔU. Looking at process A, heat is being transferred from the system to the surroundings, so the process is exothermic. In process C, heat is being transferred from the surroundings to the system, so the process is endothermic. Lastly, In process B, no heat transfer is occurring. Hope this helps!