Capt. Neal® wrote:

Again, electrons don't move THROUGH the battery.

Correct. Electrons DON'T move through the battery, but charge does.

They only reside
on physically separated plates via chemical reaction (not a circuit).

Incorrect. That's what happens in a capacitor, but not in a battery.

In a capacitor, electrons are stored on one plate and "holes" on the
other, and no electrons move THROUGH the capacitor. Nevertheless charge
APPEARS to move through it because it goes in via one wire and out via
the other, but really the charge is only stored on the plates and does
not travel across the gap. When you DIScharge a capacitor, the charge
comes back out again, but still no charge travels directly from one
plate to the other within the unit.

A battery is different. It also stores charge, but not by accumulating
more and more electrons on one plate and holes on the other, but rather
by arranging for chemical changes to occur not only on both plates, but
also in the electrolyte.

As shown in hyperphysics.phy-astr.gsu.edu/hbase/electric/leadacid.html
which you pointed us to, a charged battery starts off with the electrolyte
of sulphuric acid, i.e. a soup of negative sulphate ions and positive
hydrogen ions, and with PbO2 on one plate and Pb on the other. When
the plates are connected via an external circuit, the sulphate ions are
absorbed equally on each plate, in a reaction which at the Pb end
generates PbSO4 and liberates electrons and H+ ions, and at the PbO2 end
also generates PbSO4 and absorbs electrons and H+ ions. To sustain this
reaction, the electrons travel from one plate to the other on the outside
of the battery, via the circuit wire, while the H+ ions travel from one
plate to the other internally, through the electrolyte.

Therefore charge does travel through the battery. We have a complete
circuit, with external flow of electrons and internal flow of H+ ions.

During charging, the same thing happens, electrons are "pumped" back
into one plate and sucked out of the other, which causes the hydrogen
ions to travel through the electrolyte in the opposite direction to
that in which they travelled while the battery was being discharged.

"Ronald Raygun" wrote in message . uk...
Capt. Neal® wrote:

Again, electrons don't move THROUGH the battery.

Correct. Electrons DON'T move through the battery, but charge does.

They only reside
on physically separated plates via chemical reaction (not a circuit).

Incorrect. That's what happens in a capacitor, but not in a battery.

In a capacitor, electrons are stored on one plate and "holes" on the
other, and no electrons move THROUGH the capacitor. Nevertheless charge
APPEARS to move through it because it goes in via one wire and out via
the other, but really the charge is only stored on the plates and does
not travel across the gap. When you DIScharge a capacitor, the charge
comes back out again, but still no charge travels directly from one
plate to the other within the unit.

A battery is different. It also stores charge, but not by accumulating
more and more electrons on one plate and holes on the other, but rather
by arranging for chemical changes to occur not only on both plates, but
also in the electrolyte.

True.

As shown in hyperphysics.phy-astr.gsu.edu/hbase/electric/leadacid.html
which you pointed us to, a charged battery starts off with the electrolyte
of sulphuric acid, i.e. a soup of negative sulphate ions and positive
hydrogen ions, and with PbO2 on one plate and Pb on the other. When
the plates are connected via an external circuit, the sulphate ions are
absorbed equally on each plate, in a reaction which at the Pb end
generates PbSO4 and liberates electrons and H+ ions, and at the PbO2 end
also generates PbSO4 and absorbs electrons and H+ ions. To sustain this
reaction, the electrons travel from one plate to the other on the outside
of the battery, via the circuit wire, while the H+ ions travel from one
plate to the other internally, through the electrolyte.

Therefore charge does travel through the battery. We have a complete
circuit, with external flow of electrons and internal flow of H+ ions.

There's where I disagree. Charge does not 'travel through' the inside
of a battery. There is no conductor only chemical reactions that change
the composition of the plates. Depending on whether the battery is
being charged or discharged these reactions run one way or the other.

Note, I said the reactions run one way or the other. I did not say the
electricity flows one way or the other. There is a difference which
all you naysayers fail to comprehend. Chemical reactions change
the plate composition. Plate composition is responsible for the current
that is noted in the circuit *outside* the battery. There is no corresponding
circuit inside the battery. If there was the battery would immediately
short out internally.


During charging, the same thing happens, electrons are "pumped" back
into one plate and sucked out of the other, which causes the hydrogen
ions to travel through the electrolyte in the opposite direction to
that in which they travelled while the battery was being discharged.


Nothing in the way of current travels back and forth in the electrolyte.
The electrolyte is there only as a medium for chemical reaction not as
a highway or path for electrons to travel.

CN

Capt. Neal® wrote:

"Ronald Raygun" wrote

Therefore charge does travel through the battery. We have a complete
circuit, with external flow of electrons and internal flow of H+ ions.

There's where I disagree. Charge does not 'travel through' the inside
of a battery.

The battery is empty when all the sulphuric acid is used up and has been
turned into lead sulphate on both plates. Let's look at the battery just
before it's completely empty, when the last ten dissociated H2SO4 molecules
are still swimming around, and let's consider what happens from then until
they're all gone.

Your diagram shows the dissociation of H2SO4 as partial into H+ and HSO4-,
but in some ways it's easier to think in terms of full dissociation into
2H+ and SO4--. It makes no difference to the bottom line in terms of
charge accounting, it's just a little more confusing to work with the
partially dissociated model.

Think of these 10 molecules as spread out uniformly through the remaining
electrolyte, and let's have the battery oriented with its - terminal (Pb
plate) in the West and the + terminal (PbO2 plate) in the East, and let's
imagine the electrolyte divided into five vertical slices perpendicular
to the East-West line, and let there be two molecules (i.e. two SO4-- ions
and four H+ ions) in each slice. Call the slices A, B, C, D, E, with A
adjacent to the West plate and E to the East plate.

On average, one of the SO4-- from each slice will end up on each of the
plates, and all four H+ will take part only in the Eastern reaction.
The plate reactions a

West: Pb + SO4-- + 2H+ -- PbSO4 + 2H+ + 2e-
East: PbO2 + SO4-- + 4H+ + 2e- -- PbSO4 + 2H2O

Pragmatically, though, both SO4-- ions from both A and B will go West,
while both from both D and E will go East. From C, one will go West and
one East. But all H+ from all cells will go East.

We must have a neutral charge change within each slice, but as you'll see,
there will be charge flowing across all slice boundaries.

At the boundary between the West plate and slice A, A's own two SO4-- ions
will travel West, as will the three which came passing through from slices
B and C. Net flow across this boundary: -10 West.

At the AB boundary, we have A's 4 H+ going East, and B's and C's three
SO4-- coming West. So as far as slice A goes, we have -10 going out on
the Western front, -6 coming in from the East (subtotal -4 out), and A's
four H+ going out East. Final charge total is neutral *for the slice*,
but of course at the *boudaries* we have a net flow -10W in the W and
-6W and +4E in the East, which is equivalent to -10W.

Slice B: Its two SO4-- go West, one SO4-- passes through EW from C, all
its 4 H+ go East and A's 4 H+ pass through WE. Since all the "passers
through" cancel out, the net change to B is -4W and +4E which is neutral,
but the BC boundary has one SO4-- going West (-2W) and eight H+ going
east (+8E) which again is equivalent to -10W.

Slice C: One of its SO4-- goes West, one East. Net -4 out so far. All
its 4H+ go East. Net neutral. 8H+ passing through West to East.
CD boundary: one SO4-- East (-2E) 12H+ East (+12E). Net +10E which
is equivalent to -10W.

I'll leave what happens in slices D and E and at the D/E and E/Eplate
boundaries as an exercise.

The crux is that that no matter where you "slice" the electrolyte,
there will be charge flowing across that slice boundary, equal to -10
going West inside the battery for every -10 going East outside the
battery.

There is no conductor

The electrolyte is sulphuric acid. I think you'll find that's a conductor.
It's a water based solutions with ions, i.e. charge carriers, swimming
around in it. If more charge carriers swim one way than the other,
then you have a net flow of charge, i.e. a current, and that makes the
medium a conductor.

Ronald Raygun wrote:

The crux is that that no matter where you "slice" the electrolyte,
there will be charge flowing across that slice boundary, equal to -10
going West inside the battery for every -10 going East outside the
battery.

In particular, if you were in reality to slice the electrolyte and
block it off, by building a plastic wall in the middle of the cell,
in effect making two cells, one with just the - plate in it, and and one
with just the + plate, then no current would flow on the outside.

Deny that!!

No current would flow on the ouside *because* no current can flow on
the inside either. Blocking off the electrolyte shuts the circuit
down every bit as much as would cutting the wire.