Wednesday, May 23, 2012

Mixtures and Compounds, Reactions and Energy, and the Great Pacific Plastic Patch

Let's take the last first. Apparently the Great Pacific Plastic Patch, where ocean currents collect discarded plastic junk, has been misrepresented by use of a photo from Manila Harbor, which shows a guy paddling a boat through a layer of garbage, mostly plastic. According to Scripps Institution marine biologist Miriam Goldstein, who has actually been there, it's not like that. The plastic is there, but it's in much smaller pieces and more spread out. The danger to fish and birds, often exemplified by a cut-open stomach crammed with plastic, may be overhyped too. Read the whole thing.

That article is titled, "Lies You've Been Told About the Pacific Garbage Patch." It's not clear to me that "lies" is the right word. "Stuff that makes a better story" or "the only way I can visualize this" might be closer, the "I" being a reporter. Or it's possible that an overwrought scientist made it sound like this or provided a not-too-carefully-researched photo.

Additionally, the National Academies of Science held a colloquium on science communication and I wrote a letter to the editor of the New Yorker on errors in a story by David Owen in their May 14 issue.

I've been half-watching tweets from the NAS event. It looks like the conclusions were the usual: science reporters need a better background, scientists need to do a better job of explaining, there is little or no motivation for either.

The David Owen article, "The Artificial Leaf" (subscription only), appears to contain two common misunderstandings: what chemical compounds are and what makes chemical reactions happen. Neither is stated explicitly, but Owen's misunderstanding those two foundational concepts is the only explanation for some of what is in the article. It also appears that the scientist being interviewed, Daniel Nocera, was funning Owen, whose limitations in understanding chemistry prevented him from understanding that.

Chemical compounds are often referred to as a mixture of elements. This is incorrect. In a mixture, there is no chemical change. In a compound, there is. So sodium, a soft silvery metal that reacts wildly with water, and chlorine, a pungent and corrosive green gas, react chemically to form the rather innocuous sodium chloride, table salt. In reacting, they share electrons, a serious commitment that, if you want to express it in journalistic terms, is sort of like sex. Dog sex, where the participants get stuck together and are hard to separate.

Water is a chemical compound, not a mixture, of hydrogen and oxygen, two hydrogen atoms sharing electrons with one oxygen atom. It's not very reactive, unless you react it with something very reactive, like sodium. Or put energy into it, by hydrolysis or by using a photoactive catalyst and sunlight, which are the two methods Owen discusses.

Chemical reactions are rearrangements of atoms, but they are also rearrangments of energy. A mixture (physical mixture, not compound) of hydrogen gas and oxygen gas has more energy than does the water that results from their sometimes explosive reaction. The excess energy is given off as heat. Turning that around, producing hydrogen gas and oxygen gas from water requires an energy input. (I'm ignoring entropy for this discussion.)

Unless a reaction produces energy, it can't happen. Catalysts only facilitate reactions that will happen anyway.

Human beings run on respiration. We breathe in molecular oxygen and react it with carbon-containing fuels (fats, sugars) to produce carbon dioxide. Those reactions, very much like controlled combustion, produce heat. The combustion that runs automobiles and generates electricity also reacts molecular oxygen with carbon- and hydrogen-containing compounds to produce carbon dioxide and water.

The fact that carbon dioxide and water are the products indicates that they have little energy left to give up. This is a useful rule of thumb for judging, say, schemes to run automobiles on water. (Hint: not possible.)

Back to Owen's article. He spends a fair bit of time on the electrolysis of water because this is an analogy to what Nocera is trying to do: split water using solar energy. However, Owen gets several things wrong along the way, or finds things remarkable that are simple consequences of what a knowledgeable reporter should understand. Hydrogen is reactive, not because it is light (molecular weight? density? buoyancy? Owen doesn't say), but because of its energy relationships. It is not remarkable that water, a product of combustion, does not combust. Hydrogen is an energy carrier because energy must be input to split water.

Nocera complicates things by declaring that liquid nitrogen, that ooh-aah fuming liquid in funny jars, is necessary "to make stuff," whatever that may mean. He throws in quantum spin liquids and using microwaves "to cook chemicals" to further impress someone who must have shown his ignorance early on.

Owen kind of glances off the idea that the purpose of artificial photosynthesis is to store solar energy. He understands that the point is to make hydrogen and then burn the hydrogen, but, although he mentions that hydrogen is an energy carrier, he never seems to make the connection. I suspect that his lack of clarity stems from his ignorance of chemistry. And his portrait of Nocera might have been different if Owen had been able to tell when Nocera was joking.

Update: One more to add to this list of shame.

Reuel Marc Gerecht and and Mark Dubowitz beat the drums for war against Iran. It's a small point within their larger drum-beating, but separation science isn't subject to authority.
Western powers seem ready to concede to Khamenei the “right” to enrich uranium to 5 percent, which would, according to Olli Heinonen, former deputy director of the International Atomic Energy Agency, put Iran two-thirds of the way toward making bomb-grade uranium.
The energy put into enriching uranium to 5 percent is indeed about two-thirds of the energy needed to enrich to 90 percent. Anyone can calculate that from an elementary chemical engineering textbook. It's not necessary to cite Olli Heinonen.

Another Update: From Steve Clemons:
Fred Espenak is Scientist Emeritus for Goddard Space Flight Center, and a retired NASA astrophysicist. He is known throughout the world for his work on eclipse predictions and blogs at His website lists dates and times for future solar eclipses through the year 2020.
The ancient Mayas knew how to predict eclipses. The Babylonians knew how to predict eclipses. The tables called ephemerides list eclipses out into some long future. (I'm being lazy and not looking things up, like Steve didn't.) If Fred Espenak is a well-known astrophysicist, I doubt that it's for his predictions of eclipses.

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