1

Physics, Astronomy & Cosmology / Re: Are voltaic cells in equilibrium?

« on: 03/05/2020 23:45:38 »

An equilibrium is where there is no overall change in the composition of the system (even though individual atoms may be changing state, there will be an equal number changing in the opposite direction).

If we take the classic copper/zinc voltaic cell: for the entire time that a voltaic cell is delivering current, one electrode will be dissolving. This is not an equilibrium
- The current will only stop when the electrode is completely dissolved. Then it is in an equilibrium.

Similarly, when there is no current flowing, the cell is (almost) in equilibrium.

2

Chemistry / Re: How can I find the point where a reaction goes to the opposite direction?

« on: 02/05/2020 22:20:53 »

How can I find the point where a reaction goes to the opposite direction?

If you want a reaction to continue in the same direction, find some way to separate out the product from the input flow and catalyst.

For example, if the reaction occurs between liquids and a solid catalyst: if the product bubbles off, it will no longer be present to participate in the reverse reaction.
- In this case, the reaction won't go in the reverse direction (as long as you keep collecting the gas)

3

Science Experiments / Re: How can I convert kPa to molarity?

« on: 29/04/2020 21:12:35 »

OK I have some oxygen.
It has the same mass as a donkey, and occupies a large room.
I don't know what that is so I will call it M (in grams).
And I don't know what volume it has, so I will call that V (in litres).
And I am assuming it's at 20 C or 293K
And I have the pressure- it's 50 KPa That's close enough to half atmospheric pressure, so I'm going to call it 0.5
I know it has a molecular weight of 32, because it's oxygen.
So I have M/32 moles of O2.

PV=nRT
And n = M/32
So P V=MRT /32
Divide through by M
PV/M =RT/32
Divide through by P
V/M = RT/(32P)
Take the reciprocal
M/V= 32P/(RT)

OK that tells me M/V which is the density of the gas.
That's how many grams I have in a litre
And I was asked for the molarity- which is the number of moles in a litre.
So I need to convert mass to moles- no problem 1 gram is 1/32 moles
So the number of moles per litre is
(M/32) /V = 32 P/RT
Interestingly the 32 cancels
I can look up R
8.31446261815324×10−2   L⋅bar⋅K−1⋅mol−1
From wiki
https://en.wikipedia.org/wiki/Gas_constant
(it's important to match the units)
Call it 0.0831 L⋅bar⋅K−1⋅mol−1
Molarity (in moles per litre)  =P/ RT
P is 0.5 bar (near enough)

P/RT =0.5/(0.0831 *293)

So, the molarity is 0.0205 moles per litre

No donkeys required.


Of course, any chemist would be less of an ass.
A mole of any gas at room temperature and 1 atmosphere occupies about 24 litres
https://en.wikipedia.org/wiki/Molar_volume#Ideal_gases

So a litre is 1/24 moles ( for 1 atmosphere)
so any gas has a concentration (at 1 atm) of 1/24 moles/litre
But this gas is at 0.5 atm so there's only half as much gas.
any gas at 0.5 atm has a concentration of 1/48 moles per litre
1/48 =0.0208 molar.

But where's the fun in that?
All you need to know is the temperature and pressure, and you can calculate the molarity of a gas without knowing the molecular mass.

Which is why Bob said this

22.4 liters of gas at STP equals 1 mole.

4

Physics, Astronomy & Cosmology / Re: How to determine thermodynamically favourable electrochemical reactions?

« on: 23/02/2020 20:09:03 »

the electrons have to go somewhere, so you will need to pair a reaction that consumes electrons with one that produces them.

You can see if the pair are thermodynamically favorable by adding their electromotive forces (the reduction potential of the reaction that is consuming electrons minus the reduction potential of the half reaction that is producing them) if the number is >0 the reaction is thermodynamically favorable.

For example:

Zn --> Zn²⁺ + 2 e^– (–0.763 V for the reverse reaction)
Ni²⁺ + 2 e^– --> Ni  (–0.280 V)

taking electrons from Zn and giving them to Ni²⁺ will be favorable by 0.483 V, the reverse reaction would be uphill by the same amount.

Note that to add and subtract these voltages, they must be compared to the same reference (NHE, RHE, SHE, Ag/AgCl, Hg/HgO, etc. etc.) and the conditions have to be the same (same temp, pressure, pH, electrolyte etc. etc. etc.) if the conditions are different, then Nernst equation must be used as well.

5

Physics, Astronomy & Cosmology / Re: What information can be derived from sending an electric current to a structure?

« on: 06/01/2020 08:30:55 »

You can read about eddy current testing in this article
https://en.wikipedia.org/wiki/Eddy-current_testing

Eddy-current testing (also commonly seen as eddy current testing and ECT) is one of many electromagnetic testing methods used in nondestructive testing (NDT) making use of electromagnetic induction to detect and characterize surface and sub-surface flaws in conductive materials.

6

Technology / Re: What is the net environmental impact of biofuels?

« on: 15/03/2019 09:53:05 »

The net impact has not been impressive to date. Fossil hydrocarbons have an inherently high energy density because they have been dehydrated and compressed over zillions of years, so in principle you  can just pick up a lump of coal or a bucket of crude oil and set fire to it, whereas anything derived from recently living plants has to be harvested, dried, compressed, and possibly boiled or fermented before it becomes useable. Even domestic firewood needs more energy input from chainsaws and trucks than coal, per unit heat output, because you are handling around 50% water in the raw product.

The more subtle problem is in fact water. Fermentation produces low molecular weight alcohols which are usefully combustible (though less energy dense than diesel) but hygroscopic, and also tend to corrode many rubber and plastic parts, so there's a limit to the amount of biofuel you can use in an existing internal combustion or jet engine. It takes as much energy to build a new car as it will use in its life, so rapid fleet replacement is not energy-efficient, even if you can design an engine that tolerates low-mw fuels. Except for methane, which has a very low energy density but can be used in a petrol engine with very little conversion.

7

Physiology & Medicine / Re: How many molecules will hit a skin cell per hour?

« on: 14/03/2019 18:52:35 »

In principle you can do this yourself.
https://bmcresnotes.biomedcentral.com/articles/10.1186/1756-0500-2-158
Or, for a less sophisticated model, you can simply assume that the substance behaves as an ideal gas.

Why do you want to know?

8

Cells, Microbes & Viruses / Re: How can we find a cell inside a water solution?

« on: 11/12/2018 19:11:25 »

Craig Venter's Sorcerer II expedition travelled around the world, sampling seawater every 200 miles.
They filtered the water through different sized filters, then just sequenced any DNA they found. This gave them a good idea of what types of cells and viruses were present.

if you ever make it to the sea, and you swallow a mouthful of seawater, keep in mind that each milliliter has about a million bacteria and on the order of 10 million viruses.

See: https://en.tiny.ted.com/talks/craig_venter_on_dna_and_the_sea

9

Chemistry / Re: What are the abilities and challenges in genomics?

« on: 06/11/2018 20:26:35 »

You could start with this podcast:"Robert Green | The Promise & Peril in YOUR Genes"
https://after-on.com/episodes/016

or "George Church | Bioengineering" https://after-on.com/episodes/024

10

Physics, Astronomy & Cosmology / Re: I need a complete list of physicochemical phenomena

« on: 03/11/2018 08:16:21 »

The KEGG database from the University of Kyoto aims to provide one such list:
https://en.wikipedia.org/wiki/KEGG

There are some others here: https://en.wikipedia.org/wiki/List_of_biological_databases#Metabolic_pathway_and_protein_function_databases

11

Physics, Astronomy & Cosmology / Re: What are the properties of currently developed metamaterials?

« on: 31/10/2018 21:11:55 »

I don't understand what negative reflective factor actually means.

Then we have a problem.
The only use of the phrase google found on the internet was you in this thread.
It seem you made it up.

I'm guessing that you have got google to translate something for you.
We might be able to help more if you tell us the original phrase.

12

Physiology & Medicine / Re: What processes produce and mitigate reactive oxygen species?

« on: 27/10/2018 12:17:41 »

I don't think he's doing homework. I think he's trying to run before he can walk.

13

Physiology & Medicine / Re: What is the pathophysiology and histopathology of cataract?

« on: 07/10/2018 09:53:32 »

This is a very helpful article about the biochemistry and pathogenesis of cataract formation, which might help you.

14

Chemistry / Re: How much precious metal is needed for automotive catalytic converters?

« on: 23/09/2018 14:09:56 »

What is the size of the precious metals particles that are put in catalytic converters and what is their number so that I can calculate the total mass in a brick?

It is easier to do that the other way round.

From
http://www.specialtymetals.com/faq/

"There are between 3-7 grams of platinum group metals in a standard catalytic converter, but the amount varies based on manufacturer and model. "

I can't find any data on the size of the metal  particles. But the only bit of the catalyst that can influence the gas phase is the surface so they make that as large as possible.
To do that they use very small particles.
I would guess at a micron or less in diameter.

It may take a while to count them.

15

Physics, Astronomy & Cosmology / Re: Why water lifts in very small tubes?

« on: 23/09/2018 05:17:59 »

It's called capillary action and it has to do with surface tension.

https://en.wikipedia.org/wiki/Capillary_action

16

Physics, Astronomy & Cosmology / Re: Can we manipulate magnetic fields?

« on: 17/09/2018 00:19:56 »

          Reply # 41 , 05/09/18
This be my basic answer , however, you could do what I did in days of yore ; delve into the micro-electronics liturature and supplies parts spec.s . You could , of course track down an electronics engineer  or at least graduate student .  You could also ask yourself ; does positive repel positive , and does negative repel negative .  Continue with ; if most materials are full of dipoles , how can I use that ? If you don't let material limitations restrict your imagination , you might " do like professor do " , and come up with something , yeehaw !
....................P.M.

17

Physics, Astronomy & Cosmology / Re: Can we manipulate magnetic fields?

« on: 16/09/2018 19:43:51 »

Yes indeedy ! I run off at the mouth real good ! 
 Imagine a small lizard w/webbed feet .  To escape predators he can roll his legs reaal fast .  If a body of water is in the way , no problem , he just slaps them feet down hard and fast , and enough upward push is created to hold his body above the water , so predator foiled !
 The above analogy is to demonstrate that many small pushes can create a spectacular result .  It's just a matter of figuring out the trick ................P.M.

And would you like to answer the question now?

18

Physics, Astronomy & Cosmology / Re: What is the effect of MRI on body?

« on: 16/09/2018 11:37:54 »

... can we assume the same for iron nanoparticles? ...

The iron in tattoo-ink can be a problem ... https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3445217/

19

Physics, Astronomy & Cosmology / Re: Can we manipulate magnetic fields?

« on: 02/09/2018 16:06:29 »

Permanent magnets take energy to create; it's not possible to make them with no energy, but they do generally persist for very long periods.

The equivalent with electrostatics is called an electret:

https://en.wikipedia.org/wiki/Electret

and can store a very long lasting electrostatic charge. You can shape electrostatics with a metallic surface, to form an equipotential of arbitrary shape.

What forces can electrets generate? Similar to strongest permanent magnets?

No, electrostatic forces are usually weaker than magnetic forces, but they're not negligible and you can build generators and motors that work electrostatically.

Also, if get close to another electrostatically charge, what will happen? Will they lose their electrical properties?

No, they're fairly stable. I'm sure you can erase the charge in a powerful enough electric field, or by overheating them, but in normal use you won't.

20

Physiology & Medicine / Re: How does peritoneal dialysis work?

« on: 02/09/2018 09:54:07 »

Dialysis is indicated when a person's own kidneys fail; in an acute setting, and in chronic kidney conditions where other options may not be suitable, this is usually acheived by placing a tube into a large blood vessel and pumping blood through a partially permeable filter system that uses osmotic and concentration gradients to equilibrate and correct the blood biochemistry.

This sort of process is very invasive, takes a long time and is therefore inconvenient for the patient. Therefore, where the process needs to be carried out in the long term, doctors often elect to do continuous ambulatory peritoneal dialysis (CAPD) as an alternative, at least for a while.

In simple terms, a catheter with a tap on the end is implanted into the abdominal cavity to provide a route between the outside world and the space around the internal organs.

The patient connects this catheter to a large bag of dialysis fluid with the correct biochemical composition to correct their blood chemistry. The fluid runs into the peritoneal cavity and sits there. The patient disconnects the tap and then goes about their business. Meanwhile, the body exchanges ions and water across the membranes of the internal abdominal organs over a period of hours with the infused dialysis fluid.

After a set period of time, the patient re-opens the tap, drains out the spent fluid and then replaces it with fresh. With regular biochemical monitoring, and checks and care to avoid infection, this can be a safe and convenient mode of dialysis for many patients. Yes, the patient walks around with some extra fluid inside them, and they have a tube running into their abdomen so they need to be careful what they do to avoid trauma or infection, but on the whole this is a safe and well-tolerated procedure.

Regrettably, it is not, however, an indefinite option. With time, the peritoneal membranes thicken and develop adhesions in response to the low-grade irritation imparted by the presence of the dialysis fluid. This impairs the effectiveness of the dialysis process, eventually rendering it inadequate. It also carries a risk of other complications such as intestinal obstruction and infection.

At this point, patients normally need to move onto haemodialysis, where blood is piped to a machine for filtering. To facilitate this, a fistula is normally fashioned between an artery and a vein in one arm to provide a high-flow system so that large volumes of blood can be obtained and returned to the body rapidly to minimise the time spent on dialysis.

All of these processes take a heavy toll on a person's health and their well-being. It's also extremely expensive. As such, and where possible, patients are transplanted with a healthy kidney to free them from the burden.