the negative cathode - chemistry vs physics (1 Viewer)

[Farmerism]

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.

mkay but say you have a zinc ANODE. the zinc unergoes a reaction Zn(s) -> Zn2+ + 2e

so from this, it's actually the anode itself thats oxidising and causing the flow of electrons. the electrons dont come from the solution because.. the solution doesnt consist of solid atoms to electrons to begin with.

so yeah even chemistry contexts says that on pg 64

 

[pkc]

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.

The anode inside a battery forms the negative terminal of the battery, Its the place that dissolved ions have been oxidised and given up their electrons.

In the external circuit of a battery, electrons flow from the battery's anode back to the battery's cathode through the wiring that connects them. This is negative to positive. (Which is positive to negative if you want to talk in terms of conventional current)

 

[Farmerism]

so the electrons dont actually enter the metal from the solution as you say pkc

sorry and fuck this i think we're all just confusing eachother

i'll post an answer when i get one from a teacher or something.

 

[pkc]

mkay but say you have a zinc ANODE. the zinc unergoes a reaction Zn(s) -> Zn2+ + 2e

so from this, it's ac\0\0
?t??\0\0\0\0t??Ytself thats oxidising and causing the flow of electrons. the electrons dont come from the solution because.. the solution doesnt consist of solid atoms to electrons to begin with.

so yeah even chemistry contexts says that on pg 64

And where do the electrons go? Into the metal. That would make it the anode using the above definition.

If you modify the definition to
Anode: place where free electrons enter the metal (solid conductor).

It seems to work a lot clearer.

Hope it helps.

 

[Farmerism]

oh alright pkc i see what youre saying. so is the long thing still the positive terminal? and teh arrow that i drew, is that the direction of the conventional current then? i know this is prelim stuff. im screwed

 

[Farmerism]

wait lemi ask again is the long thing the positive terminal aka the.......cathode?

 

[pkc]

wait lemi ask again is the long thing the positive terminal aka the.......cathode?

Correct.
The positive terminal is the long line, and it represents the cathode of the galvanic cell (power source).

 

[A l]

Definitions of anode (from Dictionary.com)
- A positively charged electrode, as of an electrolytic cell, storage battery, or electron tube.
- The negatively charged terminal of a primary cell or of a storage battery that is supplying current.

Definitions of cathode (from Dictionary.com)
- A negatively charged electrode, as of an electrolytic cell, a storage battery, or an electron tube.
- The positively charged terminal of a primary cell or a storage battery that is supplying current.

In electrochemistry, when looking at a galvanic cell, the anode is assigned to be negative because it is the NEGATIVE TERMINAL. Why?....because this is where electrons come from so it is initially negative. However, as electrons LEAVE the anode, the ELECTRODE has an OVERALL POSITIVE CHARGE because there is a deficiency of electrons.
Similarly with the cathode, it is assigned to be positive in electrochemistry because it is the POSITIVE TERMINAL. Why?....because this is where the electrons come in, so it is initially positive. However, as electrons ENTER the cathode, the ELECTRODE has an OVERALL NEGATIVE CHARGE because there is an excess of electrons.
Remember that all this occurs WITHIN A BATTERY and as a result:
- cathode (electrode) has become negatively charged
- anode (electrode) has become positively charged

Using that result, in an external circuit, a battery contains a negatively charged cathode and a positively charged anode. Now we can manipulate this and extract electrons to move FROM the cathode of the battery to flow to the anode on the other side of the battery. Why?....because the cathode has been negatively charged so there are electrons hovering around the cathode (as a result of the galvanic cell above). Hence, electrons (or cathode rays) are said to flow from cathode to anode. Hence, in a circuit diagram the cathode is assigned a shorter line than the anode. Therefore the cathode is the negative terminal and the anode is the positive terminal for an EXTERNAL CIRCUIT.

NOTE: The first definition of cathode and anode only applies for galvanic cells and batteries. The second definition of anode and cathode only applies for external circuits.

NOTE: The definition states that a cathode is POSITIVELY CHARGED terminal in a power supply. This is different to a POSITIVE TERMINAL.
A POSITIVE TERMINAL is where the electrons enter as a result of attraction.
A POSITIVELY CHARGED terminal is where the terminal has become positively charged as a result of electrons leaving the terminal. This is the case of the cathode, where electrons flow from cathode to anode in an EXTERNAL CIRCUIT. Since the electrons leave the cathode and move into the external circuit, the cathode has an overall positive charge, hence it is a positively charged terminal.
The above also applies for the anode definition.

In summary:
- Electrons flow from anode to cathode WITHIN a battery
- Electrons flow out of the battery from cathode to anode in an EXTERNAL circuit

Hopefully you'll be able to follow that, otherwise it gets really confusing...

 

[Farmerism]

yeah cool thanks man

i get it now

 

[Riviet]

Very nicely explained, A l. It certainly clears everything up.