 So while looking at the idea of a second law efficiency, what we're going to be doing is looking at a new property that is called exergy. So what I'd like to do now is take a few moments to introduce the idea of exergy. So when we're performing exergy analysis or looking at exergy, first of all, exergy itself is a property that enables us to determine the amount of useful work potential that exists at a particular state with respect to some dead state. And out of convention of exergy and exergy analysis, what we do is we specify this dead state to be that of 101.325 kilopascals for pressure, which is normal atmospheric pressure, and atmospheric temperature, 25 degrees Celsius. And we also assign property information to the dead state. And that is P0, T0, H0, U0, and S0. So that would be your entropy internal energy, enthalpy and pressure and temperature at this dead state. So what we do is we look at our system at a given state, and we determine the amount of useful work potential at that given state with respect to this dead state. The concept of exergy itself is a European term that was derived in the 1950s, and it was actually preceded by a term that was coined at MIT called availability. So if you look in some thermodynamics textbooks, you may find them discussing availability and not exergy, but just be aware that they are the same thing, the same concept. And the MIT term was coined in probably about the 1940s. And what it is, it's the amount of useful work that you could get out of a system at your specified state if you were to put a heat engine between your system at the specified state and the dead state. So that is the idea of the concept exergy. And what this does, by analyzing where or how much exergy we have in a system at a given state, it enables us to determine the amount of work that we could get out of the system, reversible work potential. And we could then compare it to the actual work that we do get out of the system, and we will always have the actual work, or the useful work coming out as being less than the reversible work. But what it does is it shows us if we could improve our system, and usually we can improve it, but it will identify ways that we could improve our system. And that will come out as we do exergy analysis.