Calculating Heat Over a Cycle: Q, dU, W

[mneox]

Homework Statement

How much heat is added over this cycle? During which processes?
What is the heat expelled from d to a?

Homework Equations

http://img838.imageshack.us/img838/6270/29494670.png
(Goes clockwise, abcda)

The Attempt at a Solution

I'm just generally confused overall about this question. Is heat added in the processes which are going "forward"? So would heat only be added during processes a-b and b-c?

And would I use Q = dU + W to calculate the heat added for the processes?

For the 2nd question, for heat expelled, would I still just use Q = dU + W to find it?
So Q = nCvdT + pdV to find the heat expelled for process d to a.

Thanks for any clarification and help, I am really lost here.

 

[mneox]

Anyone?

 

[Redbelly98]

Hi. Yes, you would use Q = ΔU + W to get the heat added or expelled for each path segment. Q is positive for heat added, and negative when heat is expelled.

 

[Andrew Mason]

How does the temperature at c compare to the temperature at b? Use that to determine the heat flow from b-c.

How is the net work done by the system related to the heat in and heat out?

AM

 

[rwisz]

To calculate the heat added over the cycle, you would need to calculate the change in internal energy (dU) and the work done (W) for each process. The heat added over the entire cycle would be the sum of these values. Heat is added during processes a-b and b-c, as indicated by the positive values for dU and W in these processes. The heat expelled would be the heat added in the reverse direction, so it would be the negative values for dU and W in processes c-d and d-a. Therefore, to calculate the heat expelled from d to a, you would use the equation Q = dU + W, using the values for processes d-a and c-d. I would also recommend double checking the signs of the values for dU and W for each process to ensure accurate calculation of the heat added and expelled.