Second Law of Thermodynamics Restatement with usable energy instead of entropy Is it technically accurate to state the Second Law of Thermodynamics as:

"The total amount of usable energy only decreases in a closed system"

I ask because it doesn't evoke the term "entropy", which usually only confuses the average person.
 A: What you suggest is the so-called Exergy, a term introduced in the fifties for a concept (the available energy) that dates back to Gibbs. The decrease in exergy is the counterpart of the usual increase in entropy.
However, I notice that after more than sixty years, the concept of exergy has not substituted entropy. Entropy may be confusing for the average person, but exergy is by no means a simpler concept.
A: 
Is it technically accurate to state the Second Law of Thermodynamics as: "The total amount of usable energy only decreases in a closed (actually, isolated) system"

Yes, we can give the following qualitative interpretation of the above statement without explicitly mentioning entropy or exergy.
A non-equilibrium system is generally characterized by gradients of temperature, pressure and chemical potential. The classical example is a rigid insulated box divided into two parts, each in its own temperature, pressure, and with its own composition. If we remove the partition under the presence of gradients there will be transfer of mass and energy between the two parts until $T$, $P$ and $\mu$ are uniform. This is a statement of the second law: the tendency of an isolated system is to reach a state in which no gradients of $T$, $%P$ or $\mu$ exist.
At the same time, useful work can be extracted from a thermodynamic system only in the presence of gradients. A Carnot cycle needs two different pressures, work requires a $\Delta P$, osmotic work requires $\delta \mu$. We can produce work from a non equilibrium partitioning of the system, but not from a system that has reached equilibrium, this would have to be placed into contact with some other system at different $T$, $P$ and $\mu$. The dissipation of gradients is what Kelvin termed the "heat death" of the universe.
