the negative cathode - chemistry vs physics (2 Viewers)

[Farmerism]

okay the cathode is the negative electrode. i accept that. because cations migrate towards it in an electrolytic reaction

cations are positive charges which are attracted to the cathode thats negatively charged.

and the anode is the positive electrode because anions migrate towards it. where anions are negativly charged ions.

okay now in chemistry, with reference to galvanic cells. the cathode is positive. and i assume this is because the cations which are positive migrate to the cathodic area. making it positivly charged overall.

tell me if im wrong. cuz i only assume.

okay so. the electric current in a galvanic cell goes from the oxidising anode to the reducing cathode.

so the electron flow is from anode to the cathode.

but like..

in physics the conventional current, flow of positive charge (which i dont quite understnad cuz. cations stay where they are in the metallic structure - it is the elctrons that only move), goes from positive terminal to negative terminal. which is anode to cathode.

therefore electron flow is from cathode to anode.

how can this be? i dont get it.

 

[.ben]

i always thought anode was the negative electrode and cathode was the positive electrode?

but my chemistry teachers says anode is positive so i'm confused.

 

[pLuvia]

In galvanic cells or electrochemical cells the anode is negative and the cathode is positive. But in an electrolytic cell anode is positive and the cathode is negative.

 

[gordo]

tomato tomato

 

[pkc]

Chemistry
Oxidation always occurs at the anode, reduction at the cathode.

Physics
Cathode- plate that electrons come from (when entering the external circuit).

 

[insert-username]

in physics the conventional current, flow of positive charge (which i dont quite understnad cuz. cations stay where they are in the metallic structure - it is the elctrons that only move), goes from positive terminal to negative terminal. which is anode to cathode.

Conventional current is not really a current at all. We now know that electricity is a flow of electrons - negatively charged particles. Before this was discovered, it was assumed that it was a positive charge that moved, and various theories were developed with this erronous information. Those theories were good though, so they were kept. However, they refered to a movement of positive charges, which didn't exist, so physicists "made up" the movement of positive charges. It is the reverse of the electron flow and refered to as the "conventional current". Don't get confused: conventional current isn't actually a current - it's just useful to have it for things like the right hand rule/push rule.


I_F

 

[pkc]

As you can see there is no single rule for from and to when it comes to anode and cathode, it depends entirely on the type of device you are talking about.

 

[acullen]

The pioneers of electricity screwed up. They thought that current was the flow of positive charges through a conductor. It wasn't until experiments were done with cathode ray tubes that it was found that the charged particles were being expelled from the negatively charged cathode towards the positive anode.

Of course, the very definition of a particle's charge being "positive" or "negative" is only based around how it interacts with other charges of similar or opposite charge. It very well could have been that the pioneers could have said that electron has a positive charge and the proton, negative. The only real difference would be that any law involving charges and the cross products of vectors simply having the order of the cross product performed the opposite way. i.e.: F=q * v x B would become F=q * B x v meaning the direction of the force would be reversed.

You'll encounter a similar experience to conventional current flow when you do semiconductivity where the concept of the flow of holes is introduced. Of course it is really the absence of electrons due to their movement in the opposite direction.

One very good analogy I read somewhere was the concept of a bubble moving up a column of glass. It is much easier to think of the bubble moving up the column than it is to think of the water moving down the column.

 

[.ben]

what's an electrolytic cell?

 

[rama_v]

what's an electrolytic cell?

One which is non-spontaneous (i.e. you have to put current into the cell to force the redox reaction to occur). They are used for electrolysis.

 

[passion89]

Just know that in

Chemistry:
Galvanic cell --> Anode is negative and cathode is positive
Electrolytic cell --> Anode is positive and cathode is negative

Physics:
Anode is Positive
Cathode is Negative

 

[Farmerism]

passion89]Just know that in

Chemistry:
Galvanic cell --> Anode is negative and cathode is positive
Electrolytic cell --> Anode is positive and cathode is negative

Physics:
Anode is Positive
Cathode is Negative

okay. but why? is it something along the lines of what i said earlier, in the first post

with reference to galvanic cells. the cathode is positive. and i assume this is because the cations which are positive migrate to the cathodic area. making it positivly charged overall.

mind you a cathode is a negative electrode. according to jacaranda. so it is possible to say that the cathode is positivly charged...............

cuz i simply cant accept things like. this is this just because IT IS.......... cuz thats just stupid. theres got to be an explaination for things

and they cant say that an anode is positive in one context and then negative in another just because IT IS.... cuz yeah, it should have the same definition in any context

and the history behind the conventional current as mentioned by acullen and insert-username. thats interesting. but i dont like it. cuz that means that even in todays physics we're basing 'facts' on something thats not real......... but hey. i like the right hand palm rule. saves me from thinking too much

 

[Riviet]

A very interesting topic indeed. Acullen's response is the most related to what you are asking about. In the 18th century, they didn't know whether it was positive or negeative charges that flowed in a circuit. Also with the discovery of "cathode rays", the name is still that because that is where they thought the rays travelled towards. If you are still not convinced, I would suggest you go do some further research/reading about it.

 

[Farmerism]

Also with the discovery of "cathode rays", the name is still that because that is where they thought the rays travelled towards. If you are still not convinced, I would suggest you go do some further research/reading about it.

hm okay. well. jacaranda says

the... invisible 'ray'... originated at the negative electrode, or cathode, of the vacuum tube... Goldstein...named the rays...cathode rays

he named them cathode rays becuase they came FROM the cathode. not travelling towards it.. unlike in chem where cations are attracted to the cathode.

its so wierd. but because the cathode is a negative electrode, its easy to understnad this. but still why is a cathode postive in chem?

i keep repeating my question... have i just missed the answer?

 

[pkc]

mind you a cathode is a negative electrode. according to jacaranda. so it is possible to say that the cathode is positivly charged...............

cuz i simply cant accept things like. this is this just because IT IS.......... cuz thats just stupid. theres got to be an explaination for things

and they cant say that an anode is positive in one context and then negative in another just because IT IS.... cuz yeah, it should have the same definition in any context

If you are after a definition that applies to both physics AND chemistry try:

Anode: Place where electrons leave a metal.
Cathode: Place where electrons enter a metal.

I think it works in all cases, although I wouldnt recommend it as an answer in a HSC.

See above posts for separate definitions in physics and chemistry.

 

[pkc]

oops, other way round.

Anode: place where electrons enter a metal (or solid conductor).
Cathode: place where electrons leave a metal (or solid conductor).

 

[Riviet]

I don't think it works for the chemistry definition, in which electrons are transferred from the anode to the cathode.

 

[Farmerism]

yeah in chem oxidation, which is the loss of electrons, (meaning that the flow of electrons come from the anode) occurs at the anode. so from this 'definition' flow of electrons comes form anode

 

[Farmerism]

can someone tell me something now.

( i attached something)can someone correct me

the longer line of the cell in the circuit is the positive terminal. which is i assume the anode yeah? because the anode is the positive electrode. but is it the conventional current that flows from the anode. or is it the flow of electrons.

cuz this is what mucked up my decision when i was trying to figure out what was what.

i cant believe its taking me so long to get an answer... and i have no teachers or tutor people to call.

 

[pkc]

Read the definition carefully.

At the anode of a galvanic cell electrons enter the metal from the solution.

At the anode of an electrolytic cell electrons enter the metal from the solution.