8-6C Consider a process that involves no irreversibilities. Will the actual useful work for that process be equal to the reversible work? 8-7C Consider two geothermal wells whose energy con- tents are estimated to be the same. Will the exergies of these wells necessarily be the same? Explain. 8-8C Consider two systems that are at the same pressure as the environment. The first system is at the same temperature as the environment, whereas the second system is at a lower temperature than the environment. How would you compare the exergies of these two systems? 8-9C Consider an environment of zero absolute pressure (such as outer space). How will the actual work and the use- ful work compare in that environment? 8-10C What is the second-law efficiency? How does it differ from the first-law efficiency?