1

Chemistry / Re: How do I grow a spinel crystal?

« on: 25/06/2022 02:30:11 »

How about cobalt oxide spinel? Co₃O₄, which can be made by hydrothermal synthesis.

I found a paper (unfortunately the manuscript its self behind a pay wall, but both some of the experimental data and the cover art and abstract are available). Granted, their crystals were microscopic, but that's ideal for their application, and it looks like they worked out some fundamental kinetics of the crystal nucleation and growth vs temperature and other controllable variables...

Abstract: The hydrothermal growth of cobalt oxide spinel (Co3O4) nanocrystals from cobalt acetate precursors was monitored with in situ powder X-ray diffraction (PXRD) in combination with ex situ electron microscopy and vibrational spectroscopy. Kinetic data from in situ PXRD monitoring were analyzed using Sharp–Hancock and Gualtieri approaches, which both clearly indicate a change of the growth mechanism for reaction temperatures above 185 °C. This mechanistic transition goes hand in hand with morphology changes that notably influence the photocatalytic oxygen evolution activity. Complementary quenching investigations of conventional hydrothermal Co3O4 growth demonstrate that these insights derived from in situ PXRD data provide valuable synthetic guidelines for water oxidation catalyst production. Furthermore, the ex situ analyses of hydrothermal quenching experiments were essential to assess the influence of amorphous cobalt-containing phases arising from the acetate precursor on the catalytic activity. Thereby, the efficient combination of a single in situ technique with ex situ analyses paves the way to optimize parameter-sensitive hydrothermal production processes of key energy materials.

https://chemistry-europe.onlinelibrary.wiley.com/action/downloadSupplement?doi=10.1002%2Fchem.201801565&file=chem201801565-sup-0001-misc_information.pdf

https://chemistry-europe.onlinelibrary.wiley.com/doi/epdf/10.1002/chem.201886961

https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/chem.201886961

https://chemistry-europe.onlinelibrary.wiley.com/doi/full/10.1002/chem.201801565

2

Chemistry / Re: In what fundamental forms are energy released when hydrogen burns in oxygen?

« on: 20/06/2022 03:51:00 »

NOTE: I think this thread is more suitable for General Science as it involves energy.

I think chemical energy to kinetic energy seems problematic.

Let's assume 2 H + 1 O atoms with negligible KE in the CM frame. Somehow, they combine to give H₂O. There is no way the single H₂O molecule could acquire any kinetic energy relative to the center-of-mass frame. This would require an external force acting on the H₂O, but any forces during the formation of this single molecule may only be internal forces.

How to solve this classical mechanics paradox?     

I don't think that purely internal forces causing changes to vibrational motions would be prohibited by any conservation laws.

By analogy, perhaps could imagine an arrangement of magnets (or springs) with negligible KE in the CM frame, that when allowed to combine and "react" with each each other would result in a system with significant internal kinetic energy. This extra KE could well be in the form of a symmetrical vibrational mode, in which there is no net motion of the center of mass.

The forces involved in chemical reactions are often viewed very abstractly, but I think this is a mistake. On a molecular level, chemical reactions are extremely violent events (series of events, really), involving lots of smashing, and rending, and ricocheting. More like cars crashing into each other (repeatedly) than building with legos...

3

That CAN'T be true! / Re: hydrinos!

« on: 11/06/2022 19:42:50 »

It's 100% nonsense, as far as i'm concerned, that's not in question. How has he kept this going for 30 years? I'm beyond baffled.

Well, there are still people out there selling (and buying!) "free energy" devices... (and horoscopes for that matter!)

People are easily fooled into believing something they dearly wish to be true. And that goes for multi-zillionaire investors as well as regular folks.

It is obvious (and mathematically derivable!) to anybody who understands college-level chemistry and physics that there is no energy level below the 1s. But many people have never gone to college, and even those who have never took (or passed) any serious chemistry or physics classes, and even those who have may not really remember after a few years... Anybody without such an intimate understanding would only accept that the 1s is the lowest energy level on faith, or based on oversimplified models, either of which can be overcome by a smooth-talking charlatan. (especially since the reality is quite counterintuitive and not easily tested or examined by a typical person.)

4

Chemistry / Re: How to extract Fluoride from Mouthwash?

« on: 10/06/2022 15:31:37 »

you can buy calcium fluoride (fluorite) crystals fairly cheaply. Many of them are very pleasing octahedral shapes (for example, a quick google search shows:


Screen Shot 2022-06-10 at 10.28.34 AM.png (841.44 kB . 1466x792 - viewed 614 times)

5

Physiology & Medicine / Re: Can You Define What a Woman Is ?

« on: 10/06/2022 15:16:56 »

There is very little functional requirement nowadays for most of the human male anatomy. The likely longterm outcome is that, like some fish and spiders, evolution and food shortages will favor smaller males, gradually diminishing to genitals on legs.

You are forgetting that not all traits that are selected for evolutionarily are for survival. Attracting mates is also quite important, and many phenotypes are selected for purely for mate attraction, even when they are detrimental to survivability (see: bird plumage)

https://www.nature.com/scitable/knowledge/library/sexual-selection-13255240/

6

General Science / Re: What takes more energy walking or skateboarding?

« on: 06/06/2022 21:17:16 »

More information is needed to answer the question: same speed? I assume flat means level (no grade) and with no bumps large enough to impede the wheels (is this correct?) how smooth/slippery is it? is it windy? if so, how much, and which direction compared to direction of motion? how well-oiled is the skateboard? (one could imagine under perfect conditions a single push would allow the skateboarder to eventually make it to the end.)

7

Chemistry / Re: quick question for bored chemist

« on: 04/06/2022 01:47:41 »

Thanks for the clarification.

Yes, diazomethane has a very rich chemistry, beyond mere methylations. It is extraordinarily hazardous too: in addition to its substantial toxicity, it is prone to detonation if it gets too hot, or if it is treated roughly. There is a silylated version which is slightly easier to handle (trimethylsilyl diazomethane), being a liquid rather than a gas, but even then... yikes!

One of my colleagues in grad school referred to diazomethane as "Angry Yellow" because of its apparently ill temper and its bright yellow color.

8

Chemistry / Re: quick question for bored chemist

« on: 03/06/2022 18:56:03 »

I'm not Bored chemist, but as a chemist, would be happy to offer some insight.

I would imagine it to be equally hazardous to one's dna.

Any methylating agent with a sufficiently good leaving group will be able of damaging DNA, unless it is so good it reacts with water first or is not bioavailable (polymer supported methylating agents would be much harder to get into cell nuclei).
https://pubs.acs.org/doi/pdf/10.1021/ol025633s
http://www.arkat-usa.org/get-file/29478/

diazomethane

diazomethane is only useful as a methylating agent under acidic enough conditions to protonate the methyl group (for example, methylating carboxylic acids).

What are you hoping to methylate?

9

Chemistry / Re: How can I find the optimum ΔH and ΔS for passive T control?

« on: 01/06/2022 12:30:01 »

thank you! it will take some time to read, but it looks like you made more headway than I did, so this should be very informative!

10

Physiology & Medicine / Re: Link between supercentenarians and smoking?

« on: 01/06/2022 00:50:16 »

The key to a long life is not dying. (*groan*)

11

Chemistry / Re: How can I find the optimum ΔH and ΔS for passive T control?

« on: 31/05/2022 20:49:04 »

Thanks to Eternal Student and Bored chemist for trying to answer the questions I posed.

Hi again.

I'll try and get it done but I'm off to the big city tomorrow and I know I won't be writing much here for at least a day.

    I'm really sorry but I'm not going to get this done any time soon.

   I'm already on pages of work.   Therefore no-one will want to read it, not even @chiralSPO .
I do not have the time to complete.  I'm way behind on several other important tasks.  The whole thing is now begining to cause me some stress and that's not how a forum should be. 
   I'm very sorry @chiralSPO  but you should not wait for a detailed response from me, it would safer to assume it won't happen.

Apologies,  Eternal Student.

Thanks for trying. I do not mean to give anybody homework to stress over.

I too have gotten bogged down in the math, which is why I reached out.

I have gotten somewhere:

Assuming a two state model (A Z), the equilibrium ratio of concentrations is:

[Z]_T/[A]_T = e^{–RT/(ΔΗ–TΔS)}

Because we want ΔH–TΔS to be 0 at comfortable temperatures, that restricts the range of ΔH as a function of ΔS (or vice versa). The bigger ΔH is, the more thermal energy can be absorbed per mole of transformed molecule as T increases (and vice versa). But due to the exponential nature of the function providing [Z]/[A], there will be only a very narrow range in which there is an appreciable amount of both A and Z.

Because one is turning into the other, at a given temperature, T1, [Z]_T1 = 1–[A]_T1
K_T1= (1–[A]_T1)/[A]_T1
And then at a different temperature, T2, K_T2= (x+1–[A]_T1)/([A]_T1–x), where x is how many moles is getting converted.

amount of energy absorbed when going from T1 to T2 = ΔH•x

And then I get lost in the algebraic rearrangements when trying to get ΔH•x as a function of T1 and T2. (which then means I cannot use calc to optimize it).


I may keep banging my head against this wall for a while (hints or answers would still be appreciated). But I think the long and short of it is: there isn't really much advantage to trying for a gradual transition--it doesn't change the overall amount of energy that can be absorbed (ΔH). So, as Bored chemist says, maximizing ΔH/£ (or ΔH/$) for something with a comfortable equilibrium temperature is probably the way to go, and then just use as much as needed to keep the temp where you want it.

 

12

Physiology & Medicine / Re: Can You Define What a Woman Is ?

« on: 28/05/2022 18:28:54 »

Why oh why do some people struggle to define what a woman is ?

It depends on what the context is. The simple, men and women model is appropriate for most considerations.... But in some contexts, this oversimplified model must be extended. There are many different ways in which it can be extended, depending on what the question at hand is:

• Including age: boys, men, girls, women. And then, we have to wonder what defines the cutoff. Is it a certain age that applies across the board? (ie legal adulthood definitions for voting, driving, drinking, etc.) Perhaps sexual maturity (for which multiple thresholds could be defined), which would make sense when considering sexual activity/risks etc.

• For sports. It might make more sense to look at hormone levels. (Even without administered hormones, genetics alone doesn't necessarily dictate which hormones are produced and at which levels, and even then, the bodies might have atypical responses to hormones. For example, some people are born with XY genes, but no testes, and therefore develop as female https://rarediseases.org/rare-diseases/swyer-syndrome) If we consider administered hormones, then does a female who transitions to male compete as a female or a male? What about someone who has developed as a male and then transitions to female? Should there be more than two categories, or maybe only one? The rules should be decided for each competition, well in advance of the actual competition.

• What about for medical treatment? Just M/F is terribly oversimplified, especially when it comes to treating diseases related to sex. Ideally, doctors should know the genetic makeup, hormonal history etc. of each patient. Think of it this way: a flashlight (torch) can be on or off (simple enough, no?), but if it is off, one must know whether the switch is off, if it has batteries in it, if the batteries are installed with the correct polarity, if the circuit is broken etc. It is similar for human bodies. There are so many interconnected systems, and an apparent error can have many different causes (disease, mutation, toxic exposure, injury, etc.)

• Definitions base on body parts suffer from complications such as surgeries (as alancalverd pointed out). And sometimes, people are born as intersex, with genetalia that are not obviously assignable as strictly male or strictly female. (going off of neilep's tagline, some people are only partially inside out) https://www.healthline.com/health/baby/what-does-intersex-look-like

13

Physiology & Medicine / Re: Can You Define What a Woman Is ?

« on: 28/05/2022 18:08:24 »

Just stick with the XX chromosomes. The reproductive bits don't always work and are sometimes removed if they go very wrong, but every cell of a woman's body contains two X chromosomes and every adult member of homo sapiens with two X chromosomes is a woman.

well... there are some people who have two X chromosomes and a Y (XXY). As I understand it, they present as male, and are considered male with Klinefelter syndrome. https://kidshealth.org/Nemours/en/parents/klinefelter-syndrome.html

But yes, we should definitely avoid requiring body parts to define womanhood.

14

Plant Sciences, Zoology & Evolution / Re: Have animal reactions to mirrors and windows been studied?

« on: 27/05/2022 04:19:41 »

Well, this cat certainly appears to perceive motion in this static picture:

Perhaps just like we do:

rotsnake.jpg (613.75 kB . 1024x768 - viewed 1957 times)

15

Chemistry / Re: How can I find the optimum ΔH and ΔS for passive T control?

« on: 26/05/2022 16:54:23 »

  Could you clarify this please?   I'm not sure what your ΔG is,  is it actually ΔG° ?   Are  [Z] and [A] concentrations at equillibirum only?   i.d.k.

Thank you for engaging my intended line of inquiry and trying to clarify points of confusion :-)

I am definitely not talking about ΔG° because I am trying to compare different temperatures and concentrations.

I think that [A] and [Z] are referring only to equilibrium concentrations (at each of the temperatures under consideration), so I am thinking about K, rather than Q. In the simplest case, A Z,  K_eq = [Z]/[A], though for an acid/base case (which I mentioned in another post), B^– + A-H⁺ B-H + A, it could be K_eq = ([B^–][A-H⁺])/([B-H][A]). Another option would be a dissociation, A-B A⁺ + B^–, where K_eq = [A⁺][B^–]/[A-B]

16

Chemistry / Re: How can I find the optimum ΔH and ΔS for passive T control?

« on: 25/05/2022 23:03:16 »

I understand the original idea as using an arbitrarily large quantity of phase change material to store energy and release it only at a transition temperature. I see no problem in principle other than the vast quantity of material needed. If going for a chemical change process things become more difficult as a lot of processes that are thermodynamically favourable do not proceed for kinetic reasons. With exothermic processes there is a risk of positive feedback leading to a runaway.

Thankfully, any chemical equilibrium that satisfies the reversibility requirements stipulated are not going to be at risk of thermal runaway.

Also, while it is true that favorable thermodynamics does not require practical kinetics, for now, let's leave that wrinkle out. I am envisioning very simple, fast, and reversible reactions such as proton transfer reactions—the equilibrium of protonation states of weak acids and bases, and their conjugate bases and acids.

A-H + B A^– + B-H⁺

One can think of controlling the ΔH by selecting A-H and B with appropriate relative proton affinities, and controlling the ΔS by selecting the ratio of A-H and B. In the extreme, we can think about one of them essentially being the solvent, for example a weak acid in water, (A-H +H₂O A^– + H₃O⁺) where the hotter it is, the more the acid dissociates, pushing the reaction to the right).

But what I am most interested in at the moment, is just the math involved in figuring out how to maximize the ability of the solution to absorb/release energy over a desired temperature range.

17

Chemistry / Re: How can I find the optimum ΔH and ΔS for passive T control?

« on: 25/05/2022 03:19:48 »

Effectively, you want a system that will produce a 12-hour phase change* in the outside temperature cycle.
     * This is a temporal phase change, achieved by a physical phase change

I see what you did there :-)

18

Chemistry / Re: How can I find the optimum ΔH and ΔS for passive T control?

« on: 24/05/2022 19:47:57 »

I don't get it. Suppose I have a material that melts/freezes at room temperature. This only works once, and then it's done. Say I want to heat my building in the winter.  I have liquid 'stuff' that freezes as the room temp drops just below where I want it, so it keeps the room warm until it's entirely frozen. Now what? How am I going to get it into liquid state again? I have to turn the heater on and it has all the much more work to do since it has to melt all this nice stuff on top of actually heating the place. It seems I've saved no energy at all, so I'm not sure what you're getting at.
Heating/cooling is all about insulation, not thermal capacity. The more thermal energy that passes from the hot side to the cold side, the more energy it takes to put it back.

Sure, the use of a phase-change material would not solve this particular problem. Imagine a climate (or time of year), when the temperature changes throughout the day, oscillating between a low of 15 °C and a high of 30 °C (≈59 °F to ≈86 °F), and you would rather keep the house at 22 °C (≈72.5 °F) with minimal energy usage.

Industry, the primary consumer of resources, seems not to care. In the middle of winter I watched the power consumed by the air conditioners in the computer lab. All it needed was a fresh air fan on the roof since it was well below freezing outside, and there they are pumping heat out of the lab to the radiator on the roof, and not even into the heating system keeping the offices warm.
Another building (built for IBM) had the heater break down on an August day.  We had the doors/windows open and still had to wear winter coats because there was no heat to mix with the cold system. Temp was set just like water in houses: by mixing just the right amount of hot and cold, and not just turning off the whole system when it was cool enough. Apparently the utility bill was of no concern.

They should care. But, I would like to remind folks that the point of this thread is not to answer problems of economics, politics, or even practicality. I want to know how to express the relationships between ΔH and ΔS and working temperature range of such an equilibrium. Simple thermodynamics/algebra/calculus.

19

Chemistry / Re: How can I find the optimum ΔH and ΔS for passive T control?

« on: 24/05/2022 18:33:25 »

A more interesting (and potentially more useful) approach is to have an equilibrium mixture that has a broad working range, rather than a sharp phase transition.

Imagine a chemical reaction in equilibrium. For simplicity, we will just say there are two states, A and Z.

A Z

ΔG_forward = ΔH_forward – T• ΔS_forward

For this reaction to work, entropy and enthalpy must be opposing each other ΔH_forward and ΔS_forward must both be positive (so as temperature increases, an endothermic reaction goes forward). Therefore, ΔH_reverse and ΔS_reverse must both be negative.

As the temperature changes, the equilibrium concentrations of the product/reactant states changes, absorbing heat as the temperature increases, and releasing heat as it decreases.

ΔG = –RTln([Z]/[A])
or
ΔH – T ΔS = –RTln([Z]/[A])

Some rearranging gives:
ΔH = T(ΔS – R ln([Z]/[A]))

In the real world, both ΔH and ΔS are also both functions of T, but let’s hold off on that for now, unless someone can provide a good reason why it must be considered. (I think it should be pretty subtle across the ranges of T we are trying to cover).

We can imagine the enthalpy of the reaction (ΔH) is what we are able to select. The more positive it is, the more energy is absorbed per molecule that is transformed from A to Z (and more released when going from Z to A). But if the equilibrium lies too far to one side, we will be limited in how much energy can be handled in one direction. (ie if 99.999% is in state A at a given temperature, then only a tiny amount of energy can possibly be released when the temperature falls). If we want the system to be able to both absorb and release significant amount of heat at a comfortable temperature, the larger the ΔH term is, the larger the ΔS term must be as well (so that T• ΔS is close to ΔH when [A] is close to [Z].

So the question becomes. For a given high and low temperatures (T_high and T_low), what is the optimal choice of ΔH and ΔS, such that the system is most stable between those to temperatures?[/i]

My algebra and calculus is a bit rusty. So, while my intuition indicates that there will be a very easy way to express these trade-offs mathematically, and find the optimum values, I have not been able to convince myself that the answers I am finding are correct.

20

Chemistry / How can I find the optimum ΔH and ΔS for passive T control?

« on: 24/05/2022 18:32:34 »

This question is inspired by thinking about passive temperature control.
Please, don’t sidetrack this discussion with comments about alternative technologies, or putting on a sweater, or the pros/cons of a certain temperature, or anything about climate change. I want to keep the discussion focused on the chemistry/physics/engineering/math of optimizing a system as described in the next post (the remainder of this post is all background info pertaining to how I got to the question at hand—feel free to skip ahead)

A significant portion of our society’s energy usage goes towards heating and cooling our homes and places of business. There are many ways of passively controlling temperature inside building including insulation and reflective vs light-absorbing exteriors etc. But I want to focus this thread on materials/systems that have a mediating influence on temperature by virtue of their heat capacity (I believe “thermal mass” is the term used by architects).

Some substances have an extremely high heat capacity per unit volume. For example, liquid water; coming in at about 4.2 kJ•L^–1 •K^–1, with some minor variation across its liquid range. But this pales in comparison to the incredible latent heat of a phase change.

For example, t-butanol melts/freezes at 298 K (25 °C, or 77 °F), and has a latent heat of fusion of about 116 kJ•L^–1 •K^–1. Any room at equilibrium with a bottle of t-butanol would have a significant “thermal mass” crossing 298 K (25 °C, or 77 °F). A sufficiently large bottle of liquid t-butanol, with sufficiently fast heat exchange to the room would effectively prevent the room from dropping below 25 °C. Likewise, if the t-butanol were solid, the room could be held below this temperature. If you want a different temperature, you can pick a different substance, which will have a different melting point (and different latent heat of fusion)

The problem with this approach (ignoring issues specific to the substance of choice), is that it only works for a single temperature (very narrow temperature range). It probably wouldn’t be economically feasible to have such a large reservoir of this substance with heat exchangers etc. necessary to keep a room (or building) at a single temperature. And if the temperature at any point drifted far from the melting point, then the thermal mass of the substance would be very small compared to the latent heat of fusion.

One possible solution (no pun intended) would be to have a few different reservoirs containing different substances, with different critical temperatures. For example dmso melts at 19 °C (66 °F). So one could imagine a room that is kept between 19 °C and 25 °C with one reservoir of t-butanol and one of dmso. Or one could imagine using only one solvent, but with two (or more) reservoirs with different amounts of solute, resulting in slightly different melting points (by virtue of colligative properties).