Q: What do you mean, "can of worms about human activity and the second law"? What has that got to do with simple old rusting iron?
A: Mainly that we usually don't want it -- except for iron ore (which is a mixture of dirt or rock that has a lot of iron rust , i.e., iron oxide, in it). We really like millions and millions of tons of that because it's worth millions and millions of dollars! But before we start digging in an iron mine, let's look at how we humans use the second law for our purposes. Whenever we run a truck or any kind of engine, we're using the second law for our benefit:

[Note! From here on when I write "the second law", it is using those words as a code phrase or shorthand for "what the second law describes", namely: "some process in which energy disperses or spreads out"]

      taking energy inside of substances that tend to spread out, but can't because of Ea, 
             (i.e, a high-energy mixture like oxygen (of the air) plus liquid gasoline (or solid coal),
     giving it the necessary activation energy (a spark or a flame or heating at high pressure),
     having the diffusing energy (in the form of hot expanding gases of CO2 and H2O) push a piston that turns 
            crankshafts, gears and wheels (with the exhaust gases, still fairly hot, but no longer
            available for any more piston-pushing in this engine going out the tailpipe).

So in this example, it looks like the second law is a good deal for us. It is, whether in engines or in our biochemistry (where oxygen plus food is the concentrated energy source -- but with totally different "sparkplugs" in our bodies to start our oxidation reactions that are far more controlled and in very tiny quantities compared to the violent explosions in a car engine!) Nature's second law predicts that the energy concentrated inside a chemical mixture like oxygen with oil or coal (or food) tends to spread out. It will do so, if that necessary little energy push to overcome an activation energy barrier is applied to that kind of high-energy mixture compared to the lower energy products of CO2 and H2O.

    We make our whole technological world run by grabbing as much as we can of the energy flow available from concentrated energy mixtures like oxygen and fuels to run an infinite variety of machines, electrical generators and vehicles. (Our bodies, as we have said, use second-law energy flow from the oxidation of food for the synthesis of essential compounds and for all activity, from biochemical to muscular to mental.) However, when we change energy from one form to another, from energy in a fuel plus O2 to pushing a piston or even water running down from Hoover Dam to the dynamos below, it is impossible for us to get to use all of the energy in the concentrated energy source for the jobs we want it to do. Some always is diverted as the unusable energy due to faster moving molecules (i.e., "heat") to the environment. (That's where our body gets heat to maintain our 98.6º F/37º C.)

Q: OK, I get it. Every time I start our car, I'll think of the energy the gasoline's giving out by reacting with oxygen, making hot gases, pushing those pistons and turning that crankshaft….

A: And every time you breathe, don't forget the oxygen going all over your body and …well, let me do some more summarizing before talking about that biochemistry angle a little more:
     This minute all around the world there are tens of thousands of people who are "using" (transforming to mechanical work, losing some to waste heat spread out to the environment) the concentrated energy of a mixture of oxygen with coal, oil or gas to dig up the iron ore with giant scoops and transport it via trucks, trains, and ships from different mines to steel mills. Then, more energy is used by more thousands of people to change it into iron and finally to shiny steel...What a long parade of actions based on using the second law to get what we want!
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Every step from the original rusty dirt in the ground requires transformation of concentrated energy (of oxygen plus coal, oil, gas) to do a lot of mechanical work (along with that dispersing of less concentrated energy in the hot exhaust gases of CO2 and water). Then bringing together thousands and thousands of tons of ore, coal and limestone to one place, the steel mill, is another enormous expenditure of concentrated energy in fuels (not counting the human effort in muscle and brain). Next, a totally different variety of energy transformation is done, changing the iron (oxide) ore to almost pure iron metal that has a larger internal energy content in its bonds than does the iron oxide. Wait a minute! Doesn't it seem against the second law to force a dispersed-energy chemical like iron oxide to change into a concentrated-energy chemical like nearly pure iron? Sure it is, but there's no problem. Just as in running all those truck, train and ship engines, we can take energy flow from a spontaneous process (here in this case, from two chemical processes):
The spontaneous reaction of carbon from coal with a little oxygen to form CO whose molecules are moving very fast (i.e., are very hot), followed by
the spontaneous reaction of CO with iron oxide to form fast moving CO2 molecules plus pure iron and cause the nonspontaneous change of iron oxide to iron. Of course, in doing that we will lose a large flow of energy as waste heat. To give an idea of the size of it in iron making, a ton of near-pure carbon (coke from coal) reacts with four tons of air at around 1000 C in a blast furnace to form a ton of pig iron from two tons of ore. The energy price is six tons of hot flue gas that the process spews out, some of which isn't available for more changing of iron oxide to iron. Pretty big operation.

    Did we beat the second law? No way. But by using the second law (taking the energy from two spontaneous "downhill" reactions and transferring much of it to force a nonspontaneous process to go "uphill" energy-wise and make something), just as we take gasoline energy and change some of its energy into mechanical energy (to make pistons, crankshafts, and driveshafts turn the car wheels), we got what wanted: iron from which we can produce steel, the structural material for a near-infinite number of useful objects. Better than rusty dirt, right?

Q: Are you trying to make an iron man out of me?
A: No, no. Stick to the triathlon for that. The reason I went so long on that kick of ore to iron is that it's a perfect summary of the tremendous variety of what humans can do with the aid of the second law.

    We gather objects and mixed-up raw materials from all over the world. Just bringing stuff of all sorts from so many widely separated places to one spot as in iron and steel making is certainly not a probable occurrence in inanimate nature! It's a human act, especially when you consider the further elaborate arrangements that we make with all varieties of matter, from lining up botanicals in a National Arboretum in Washington, DC to joining metal and many other kinds of materials into building a skyscraper in Chicago or a Getty Center in LA: Those are big things.

    Equally as spectacular are the human actions in smaller things, bringing together the materials and fabricating a Boeing 747 or a jet engine with so much power that a couple of them could move a Titanic. Gathering, arranging, building, fabricating -- in all of these we use (what we can of) the directional energy flow from spontaneous chemical reactions such as the oxidation of petroleum and coal.

    Let’s finish this recap of human use of the second-law energy flow: Besides making concentrated-energy chemicals like pure metals -- iron, copper, chromium and silver -- from their diffused-energy ores (and innumerable objects from them), we make thousands of other high energy substances for our pleasure or our needs. Minor things like flavors for foods. Important pharmaceuticals that save millions of lives. It may take dozens of reactions (milder than that violent one for iron from iron oxide!) to change starting materials stepwise to the final chemical product, but the overall process involves diverting energy from spontaneous 'downhill' reactions to make the 'uphill', more concentrated-energy substance that we want.

Of course, this is the kind of coupled process (i.e., a spontaneous + a non-spontaneous) that nature uses – taking a tiny bit of sunlight energy and, with the aid of extremely complex processes in organisms like plants, changing lower-energy carbon dioxide and water and traces of minerals into thousands of higher-energy substances. But don’t think that "natural" or "from natural materials" has something to do with good or harmless! There are hundreds of harmful or even poisonous chemicals in nature – from strychnine to the extremely deadly compound in simple castor beans. (Also usually omitted when someone extols the beneficial qualities of everything "natural" is the fact that all terribly toxic viruses and bacteria are totally natural!)

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