As this example shows, the value of W depends not only on the initial and final
states of the system, but also on the path between the two. In general, different paths
give different values for W.
Questions 12-13
For the previous P−V diagram,- Find the work done by the system for the path abda.
- Find the heat absorbed by the system along this same path.
Here’s How to Crack It
- From the previous problem, we learned that, for the process ab,
W = 3,000 J and for process bd, W = 0. Since W = 2,200 J for the
process ad, then W for da would be −2,200 J (ΔV is negative.)
Therefore, the total W = 3,000 J − 2,200 J = 800 J. - Since U depends on the state of the system, for any closed path
on a P−V diagram, ΔU = 0. Since ΔU = Q − W, we have 0 = Q −
800 J, therefore Q = 800 J.