Fridge Decision

[smileypete]

An ex physiscs teacher?

 

So................ (regarding another thread - please answer all questions)

 

Question 1. How much energy does it take to electrolyse 1 mole of water?

 

A. 2.76MJ

B. 237kJ

C. 14.8 volts

D. 1 amp.hour

In a fully charged lead acid battery, it's about 480kJ.

 

cheers,

Pete

[Gibbo]

In a fully charged lead acid battery, it's about 480kJ.

 

This is a mutiple choice examination. The answers have been checked by the examining board. If you think the answer is not one of the options given you are mistaken. Please select one of the answers A. B. C. or D.

 

Gibbo

[smileypete]

This is a mutiple choice examination. The answers have been checked by the examining board. If you think the answer is not one of the options given you are mistaken. Please select one of the answers A. B. C. or D.

At a cell voltage of 2.466V (14.8V for a 12V battery) it takes 479.52kJ to electrolyse 1 mole of water.

 

Eg:

 

Take a fully 12v charged battery, put in 480kJ charging at 14.8V, it will electrolyse 1 mole of water.

 

Ask a physicist if you like.

 

cheers,

Pete.

Edited May 27, 2009 by smileypete

[Gibbo]

At a cell voltage of 2.466V (14.8V for a 12V battery) it takes 479.52kJ to electrolyse 1 mole of water.

 

Eg:

 

Take a fully 12v charged battery, put in 480kJ charging at 14.8V, it will electrolyse 1 mole of water.

 

Ask a physicist if you like.

 

So far I've asked 3 and got figures between 271kJ and 286kJ.

 

Show me how you arrive at 480KJ. I'll be even happier if it's true because that means Chris W's figures are out by 20 fold instead of 10 fold.

 

Gibbo

 

Edit: The figures quoted above are before duducting the energy acquired from entropy of about 48KJ per mole.

Edited May 27, 2009 by Gibbo

[Cosmic]

The reaction is

 

2H₂O -> 2H₂ + O₂

 

The bond energies are

 

H-O : 459 kJMol^-1

H-H : 432

O=O : 494

 

So the total energy is 459*4 - 494 - 432*2 = 478 kJ

 

But that is for two moles of H₂O,

 

so the energy per mole is 239kJ

[smileypete]

So far I've asked 3 and got figures between 271kJ and 286kJ.

 

Show me how you arrive at 480KJ. I'll be even happier if it's true because that means Chris W's figures are out by 20 fold instead of 10 fold.

It depends entirely on cell voltage. 237kJ/mole assumes the lowest theoretical cell voltage of 1.23V.

 

So a cell voltage of 2.466V will use correspondingly more energy applied to the cell, to electrolyse the water.

 

So at a cell voltage of 2.466V, electrolysis of 1 mole of water would require 480kJ.

 

cheers,

Pete.

[Gibbo]

The reaction is

 

2H₂O -> 2H₂ + O₂

 

The bond energies are

 

H-O : 459 kJMol^-1

H-H : 432

O=O : 494

 

So the total energy is 459*4 - 494 - 432*2 = 478 kJ

 

But that is for two moles of H₂O,

 

so the energy per mole is 239kJ

 

 

At last someone who actually knows what he's talking about!

 

Gibbo

 

It depends entirely on cell voltage. 237kJ/mole assumes the lowest theoretical cell voltage of 1.23V.

 

So a cell voltage of 2.466V will use correspondingly more energy applied to the cell, to electrolyse the water.

 

There's your mistake, right there.

 

The electrolysis voltage is in series with the battery cell natural voltage. (model it in series as a separate cell)

 

From.....

 

http://www.stardrivedevice.com/electrolysis.html

 

"The most important fact upon which our discussion will be based is that it takes 237.13 kJ (237,130 joules) per mole of electrical energy to synthesize hydrogen by electrolysis of water, regardless of the applied voltage or the net efficiency of the cell"

 

Note that any other energy that has be thrown at the cell doesn't go into electrolysis. It could heat the electrolyte up, or heat the electrodes up, or destroy the electrodes, but the electrolysis energy is always the same at 237kJ per mole.

 

Gibbo

[Bones]

Moles are relatively small (or the one on my roof is), I am not sure they suffer from flatulance as you suggest, but lets pretend they do as this is probably the easiest way to capture hydrogen from a Mole without causing it too much greivience or putting yourself on the ALF hit list.

 

So, take one mole, make sure it suffers from flatulance (we will be using the smell here) then rig up a 'fart collecting tube'. Now, we all know the smell is hydrogen sulphide and that has 2 hydrogen atoms. As we are talking of normal pressure and normal temperature rather than a particular time period, I think we should collect an average of 10 samples in different tubes, process out the hydrogen then take our measurements from the average. Remember the size of a mole varies too, so we should collect 10 moles and do the same.

 

Once we have the average size of a mole, and the average size of a mole flatulance sample, we can then calculate how much hydrogen would be required to fill the empty space of the mole.

 

Unfortunately I only have one dead mole which has made experimentation quite hard, but i think from my calculations it is possible to determine that the answer to question 3 is 1litre

 

I was unclear about how to calucate a mole of water in CC so I used my sisters old moped as an example it is a 90cc and the tank holds 5litres dividing 90 by 5 = 18cc to the litre. As a mole is about a litre of hydrogen and I think a mole is about 18g in weight I think the answer to question 2 must be 18cc

 

I think question 1 is silly: Everyone knows it takes a bit of petrol, a bit of paper and a match to burn a mole. But if we have to be sensible, the only one that involves killing is B

 

 

ah - just noticed this is something to do with physics, not biology. Sorry!

 

 

edit:

 

 

DAMN! You just posted the answer... and amazingly enough I was right....! PHysics... my arse!

Edited May 28, 2009 by Bones

[Gibbo]

So who's up for answering the other 2 questions?

 

Gibbo

[Bones]

So who's up for answering the other 2 questions?

 

Gibbo

 

 

just did.

[Gibbo]

just did.

 

66%

 

Must try harder (or see me after school )

 

Gibbo

[smileypete]

Note that any other energy that has be thrown at the cell doesn't go into electrolysis. It could heat the electrolyte up, or heat the electrodes up, or destroy the electrodes, but the electrolysis energy is always the same at 237kJ per mole.

I agree, which is why I said:

 

'Take a fully 12v charged battery, put in 480kJ charging at 14.8V, it will electrolyse 1 mole of water.'

 

Only 237kJ will go into electrolysis, the rest will turn into heat.

 

But it still needs 480kJ total energy applied to the battery.

 

cheers,

Pete.

[Bones]

66%

 

Must try harder (or see me after school )

 

Gibbo

 

not bad for a biologist (oh, I am not one of those either!). (it is 22l)

 

 

I shall see you after school

Edited May 27, 2009 by Bones

[Gibbo]

I agree, which is why I said:

 

'Take a fully 12v charged battery, put in 480kJ charging at 14.8V, it will electrolyse 1 mole of water.'

 

Only 237kJ will go into electrolysis, the rest will turn into heat.

 

But it still needs 480kJ total energy applied to the battery.

 

cheers,

Pete.

 

Shud o' worded yer answer be''er then!

 

The question was:-

 

Question 1. How much energy does it take to electrolyse 1 mole of water?

 

A. 2.76MJ

B. 237kJ

C. 14.8 volts

D. 1 amp.hour

 

It wasn't a different question. It was what is written above.

 

So you agree that the energy thrown at the battery isn't all going into electrolysis? It's going somewhere else?

 

Odd that, because someone else's several pages of algebra proves that it is. But the same energy is also doing other things at the same time. Thus proving that free energy is just a simple matter of getting some simple sums wrong.

 

 

Gibbo

[Cosmic]

I think a mole is about 18g in weight I think the answer to question 2 must be 18cc

Despite their slight stature, moles can suffer serious flatulence, a single mole producing as much as 22 litres of gas. They therefore have to be able to withstand enormous pressures. This is the main reason that hydrogen is not commonly used as a fuel - the danger from exploding moles. So if you need to dispose of that dead mole on your roof, please make sure it's properly deflated first.

 

BTW My dad says he's got a mole in his garden but I can't believe he's counted them all.

[Peter R]

Thanks Bones - that was the best laugh i've had for quite a while, but I don't know what Moley's going to say about all these experiments

[Tom6]

For someone not living aboad then its even more questionable about whether a fridge is really needed at all. Uht milk might taste a bit funny and you might not always be near enough local shops but most of what people keep in fridges are fine for a couple of days outside a fridge. Things like real butter (salted) might even be better for it. Also canals tend to be pretty chilly so perhaps a weighted perhaps waterproofed ziplock bag on a rope might provide ample storage? Probably not a good idea while moving along but overnight?

Edited May 31, 2009 by Tom6

[Cosmic]

Yes, I think that's a possibility, though I don't know how successful/effective it tends to be. The LILO site has a few other ideas too. I think some of these have been discussed before, so it may be worth searching the archives for other people's experiences.

[alan_fincher]

For someone not living aboad then its even more questionable about whether a fridge is really needed at all. Uht milk might taste a bit funny and you might not always be near enough local shops but most of what people keep in fridges are fine for a couple of days outside a fridge. Things like real butter (salted) might even be better for it. Also canals tend to be pretty chilly so perhaps a weighted perhaps waterproofed ziplock bag on a rope might provide ample storage? Probably not a good idea while moving along but overnight?

I guess it depends on your lifestyle, and what you consider important.

 

I don't place great demands on living on a narrowboat, and can survive with some of my facilities being either rudimentary, or just plain non existent.

 

But the one summer I tried to live on a boat with no fridge, and to try and cobble up work-arounds was a total disaster. Without one milk turns rancid in hours, and butter just forms a pool on the floor.

 

So I can exist with no TV, a basic bucket loo, and very little fit-out, but I absolutely must have my fridge. Only a watertight shell and an engine are more important, in my view.

 

Personally I like gas fridges, which, if regulations allow, I would always have in preference to any form of electric one.

[Tom6]

lol, i think i remember that summer!

 

By 'questionable' i meant weigh up what you want and need and would like and how much effort you're prepared to put into it and the benefits of potentially having the extra space. I didn't mean its wrong to have one.

 

For me i would have to switch to ale rather than lager because warm lager is really unpleasant but ale is usually fine. I prefer bitter luckily. I have to admit that i seldom have butter anyway and am getting used to uht milk slowly, once opened it lasts about a day but i tend to have finished it before then. Unopened it just seems to last forever. Crucially i don't live on a boat full-time, just about a week a month and that makes a huge difference.

Edited May 31, 2009 by Tom6

[chris w]

Warm "Pol Roger '96 Winston Churchill" ........... to what is the world coming?

 

Chris

[mrsmelly]

For someone not living aboad then its even more questionable about whether a fridge is really needed at all. Uht milk might taste a bit funny and you might not always be near enough local shops but most of what people keep in fridges are fine for a couple of days outside a fridge. Things like real butter (salted) might even be better for it. Also canals tend to be pretty chilly so perhaps a weighted perhaps waterproofed ziplock bag on a rope might provide ample storage? Probably not a good idea while moving along but overnight?

 

Ye Gods

How sad of course EVERYONE needs a fridge sod the boring milk and butter problems how the hell else do we keep Beer and Cider cold eh ?

[FadeToScarlet]

I've not got a fridge at the moment.

 

Well, I have got one, but it uses so much power that I don't bother running it.

 

I tend to buy a pint of milk on my way home from work, which does morning tea and breakfast cereals. I've got UHT for emergencies should I forget, but it's not as good as the real thing.

 

I buy bacon and meat etc. just before cooking it.

 

It's annoying in some ways, because I have to keep an eye on what I've got and remember to buy things, and I can't necessarily use "Multibuy" offers- i.e. buy one bacon, get one free, as I can't keep the second.

 

But it's a lot easier than having to fit my life in the evenings around generator running and battery charging!

 

Edit: Beer and cider go onto the baseplate, when they achieve water temperature.

Edited June 1, 2009 by FadeToScarlet

[Tom6]

Blimey i've just been looking at costs of 12Volt fridges and somewhere between $400 and $1,000 seems about normal! I was hoping to find something about large enough for a couple of white wine bottles and costing about £50 & only out of idle curiosity but i guess i was in fantasy land again

Edited June 20, 2009 by Tom6

[sueb]

Get a gas fridge. Ours came from ebay and we have a carbon monoxide alarm. Sorted.

Sue