Wikipedia:Reference desk/Archives/Science/2016 April 11

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April 11

Heat of deuteration and tritiation reactions

What are heat of the following reactions of deuteration and tritiation of water or heavy water by neutron capture?

H₂O + n → HOD

HOD + n → D₂O

H₂O + 2n → D₂O

D₂O + n → DOT

D₂O + 2n → T₂O

Are they exothermal or endothermal reactions? Is there some additional experimental complication in measuring the heat of these reactions compared to ordinary chemical reactions?--5.2.200.163 (talk) 13:24, 11 April 2016 (UTC)

This book discusses the mechanisms and energies of neutron capture by protium to form deuterium. --Jayron32 13:42, 11 April 2016 (UTC)

What pages exactly? 391? Are they included in the free preview? Is the mentioned value of 2.23 MeV measured or calculated based on some (semiempirical) formula considering neutron binding energy?--5.2.200.163 (talk) 14:28, 11 April 2016 (UTC)

Is the formation of sodium-23 somehow included in the non-free preview?--5.2.200.163 (talk) 14:31, 11 April 2016 (UTC)

There is a thermodynamic isotope effect, though one hears much more about the rather modest kinetic isotope effect. [1] points me to a review by Galimov about it, only Google is not smiling on me today to tell me what that reference is. I should search on Sci-Hub, but generally prefer to make my interlibrary loans from the library wifi.

As written the reaction seems unlikely to be measured directly, as I assume the velocity of the neutron will blast the proton right out of the water molecule. There are two components: the thermodynamics of making D or T, and the thermodynamics of the exchange. The former is with very high energy and the latter with very low, so I assume that as written, your reactions can be replaced with bare H+, D+, and T+ transmutations for the same result as best as it can be measured. Wnt (talk) 14:38, 11 April 2016 (UTC)

Just to also expand on Wnt's solid answer, and clarify something: the thermodynamic relationships are state functions dependent only on the the starting and ending states, and thus independent of the path taken between the two states. The kinetic relationships DO depend on the path taken. In this case, given the fact that both deuterium and protium are stable, there is likely not a huge difference in potential energy between the two, so I would expect the thermodynamic changes (i.e. if they are exothermic or endothermic) to be relatively low. The kinetics are a different story; there may be a VERY large activation energy for the ¹H + n --> ²H reaction, but this is entirely independent of the thermodynamics. A reaction COULD be exothermic, and still have a very large activation energy. --Jayron32 18:45, 11 April 2016 (UTC)

The activation energy of this reaction is close to zero as even thermal neutrons are easily captured with a cross-section roughly equal to the geometric cross-section of proton. Ruslik_Zero 20:35, 11 April 2016 (UTC)

Well, there ya go. --Jayron32 14:48, 12 April 2016 (UTC)

Hmmm... suppose you softly putt a neutron into a proton. According to [2] and [3], the two should emit a 2.2 MeV gamma ray representing the binding energy. The momentum of this is 2.2 MeV/c = something like 12 x 1000 x 10−28 kg⋅m/s (see electronvolt table). The proton mass is 1.672621777(74)×10−27 kg, so that means the "kick" from this photon emission ought to send the nucleus recoiling just under 4000 m/s - I think. (I'm not 100% sure this logic is valid but I vent it for your delectation) This is faster than generic figures for water motion at room temp [4], but I haven't figured out just yet if it means the molecule will explode. In any case though I suppose it's a "heat of deuteration", if you can figure out what it means. Wnt (talk) 20:19, 13 April 2016 (UTC)

Is there such thing as non-radiative neutron capture?--5.2.200.163 (talk) 13:07, 15 April 2016 (UTC)

I think that the possible emission of gamma rays should not be confused with heat. Also the neutron capture must be decoupled (being separate reactions) from gamma emmision, as it is decoupled from alpha and beta radioactivity induced by it, as mentioned in neutron activation about Co-59.--5.2.200.163 (talk) 13:16, 15 April 2016 (UTC)

Masturbation and Finasteride

Does masturbation decrease the efficiency of Finasteride? — Preceding unsigned comment added by 182.18.177.78 (talk) 16:29, 11 April 2016 (UTC)

I can't imagine there's any possible reason it would...I've never heard of such reducing the efficacy of any medication...did you read this somewhere and can cite? 68.48.241.158 (talk) 17:49, 11 April 2016 (UTC)

There seems to be a common myth that masturbation can contribute to hair loss [5] [6] [7] (see [8] [9] [10] for some examples of the myth in action). So the idea is perhaps not surprising. However as I said, the link seems to be a myth i.e. there's no scientific evidence for it as with many other rumours about masturbation. Given that there's no evidence masturbation affects hair loss and the mechanism of action of finasteride doesn't suggest any particular reason to think use of the drug will be affected by masturbation in some other way, there's no particular reason to think masturbation will affect efficiency of the drug. P.S. I don't think there's any reason to think testosterone levels will affect finasteride but in any case AFAIK the effect of masturbation on testosterone levels is also fairly complicated [11] [12] [13]. P.P.S. If you are taking finasteride you should speak to an appropriate medical professional if you have concerns about any possible interactions or side effects. P.P.P.S. I should perhaps also clarify I'm mostly thinking of something "resonable". If you're an adult masturbating an average of 20 times a day perhaps while watching a lot of porn and it's causing significant physical and psychological effects, then it's possible it could affect hair loss in some way. Nil Einne (talk) 19:56, 11 April 2016 (UTC)

(ec) Finasteride is a medication primarily for treating enlarged Prostate in men. Its reported possible side effect of diminishing libido is reported by the FDA who advise not to stop taking the medication without first consulting with one's health care provider. Masturbation has been purported to have many harmful effects, especially in the stigmatizing views of the Victorian era but today's medical consensus is that it is a medically healthy and psychologically normal habit. It is considered abnormal only when it inhibits partner-oriented behavior, is done in public, or is sufficiently compulsive to cause distress.(ref.). AllBestFaith (talk) 20:03, 11 April 2016 (UTC)

The question is not about the effect of Finasteride on the body or baldness. But of masturbation on Finasteride.--Scicurious (talk) 23:26, 11 April 2016 (UTC)

But if masturbation increases testosterone levels, and the goal of finasteride is to reduce testosterone level, wouldn't that count as an interference? Scicurious (talk) 21:42, 11 April 2016 (UTC)

Not unless there are citations to that effect. -- Jack of Oz ^{[pleasantries]} 23:06, 11 April 2016 (UTC)

Well there is a link between DHT and baldness: [[14]], and there are some endocrine effects linked to masturbation habits: [[15]]. Add to it that according to finasteride, it "prevents conversion of testosterone to dihydrotestosterone (DHT)." So, it's not too mad of a supposition that it could be a visible effect between masturbation on the effect of Finasteride. Scicurious (talk) 23:26, 11 April 2016 (UTC)

But if masturbation increases testosterone levels, and the goal of finasteride is to reduce testosterone level, wouldn't that count as an interference? Scicurious (talk) 21:42, 11 April 2016 (UTC)

Well, see, there's your first mistake — that's not the goal of finasteride. See the finasteride article. It's not meant to reduce testosterone levels at all. It's meant to inhibit the conversion of testosterone into dihydrotestosterone. --Trovatore (talk) 02:30, 12 April 2016 (UTC)

See response above. -- Jack of Oz ^{[pleasantries]} 02:22, 12 April 2016 (UTC)

But there are two common uses of finasteride. One of them is to reduce hair loss. If masturbation affects hairloss then it's possible that masturbation would also affect the efficiency of finasteride in reducing hair loss. If the OP is under the misapprehesion that there is a correlation (let's ignore for a minute that this doesn't imply causation), then this may be at least part of the reason they ask. So it's important for the OP to understand there's no good reason to think masturbation does affect hair loss i.e there's little scientific evidence despite the common claims.

I don't bring this up in isolation, in fact while I'd heard of propecia (but I didn't know the International Nonproprietary Name) and had a small amount of knowledge of hair loss (in particular the effect of DHT), I'd never heard of this particular rumour before today. The only reason I know now is because I wondered like the first IP to reply why the OP might believe that, and so I searched the two keywords in the OP's question. And from that I found this rumour seems to be the most common reason why people bring up masturbation in relation to finasteride e.g. [16]. (The other reason is some people seem to think they should masturbate or not because of the possible sexual side effects of finasteride. However other than being seriously faulty reasoning, this seems irrelevant unless you're going seriously off-label with your use of finasteride.)

The other relevant point which I also already addresses is whether masturbation will have an effect on the mechanism of action of finasteride. Firstly, as has already been said by others, you're mistaken about the mechanism of action of finasteride. It's purpose is not to reduce testosterone levels. In fact, it may have a small increase because it inhibits the coversion to DHT, although regulation of the human endocrine is complex enough I wouldn't assume this without good evidence. Second, as I already said, the effect of masturbation on testosterone levels is complex and it's too simple to say it increases or decreases them.

Note getting back to the first point, unless there's evidence the changes in testosterone levels that may be caused by masturbation can cause changes in levels of conversion to DHT, there's still no reason to think the efficiency of finasteride will be affected anyway.

P.S. I didn't directly address the other common use of finasteride, although the mechanism of action issue will apply to all uses. I didn't come across any mention of concerns about a connection between masturbation, benign prostatic hyperplasia and masturbation; so it seemed far less likely this would be the cause of the OP's confusion.

Nil Einne (talk) 12:21, 12 April 2016 (UTC)

Finasteride inhibits 5 alpha reductase but not completely and 5AR converts a percentage of Testosterone to DHT. So if T increases and still 5AR is inhibited the remaining 5AR will convert that larger amount of T into DHT. At the end percentage depends on the amount... that is my issue. — Preceding unsigned comment added by 182.18.177.78 (talk) 04:28, 15 April 2016 (UTC)

momentum/weight

If an object (say on dry land, maybe a car) is traveling, the faster it moves it gains more momentum. What happens to the weight of the object (car?) Does the weight become displaced the more momentum the object generates? 199.19.248.20 (talk) 23:20, 11 April 2016 (UTC)

The weight of a car - the force exerted on it by gravity - depends only on its distance from the centre of the Earth, which won't vary significantly if it stays on the ground. The mass of the car depends only on what it's made of - for a car with an internal combustion engine, the mass will steadily decrease as the fuel is used up, but this isn't directly related to its speed. However, the vertical force exerted on the ground by the car - which might be thought of as "weight" - will vary with speed, depending on the aerodynamics of the car's body. Tevildo (talk) 00:09, 12 April 2016 (UTC)

In the strict interpretation of mass energy equivalence, I believe given two identical cars, where one is traveling faster than the other, the faster one will have more kinetic energy and will therefore have more mass and weigh more! Mass_in_special_relativity#Relativistic_mass. However for any speed which is not within an order of magnitude of the speed of light, the increased mass can pretty much be ignored, as it would be infinitesimal. Vespine (talk) 03:43, 12 April 2016 (UTC)

I could be totally wrong, but after a little playing with some online energy calculators, you would need 1,000,000,000 (one thousand million) 1 ton cars traveling at 100km/h to increase the relativistic mass of the whole system by 4 grams. Vespine (talk) 03:50, 12 April 2016 (UTC)