flow of electrons and current question

[beponychick]

Hey guys,

one more quick question...

I know that in a circuit, electrons travel in the opposite direction than current (I) does. But which direction is it? Do electrons travel from higher voltage to lower voltage (and current travels from lower to higher) or the other way around?

Thanks!!!

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[Jezzielin]

Hey, someone correct me because I could be wrong...

In a galvanic cell the anode is negative and the cathode is positive, the electrons go towards the positive, thus the current flows in the opposite direction.

In a electrolytic cell the anode is positive and the cathode is negative, the electrons go towards the positive, thus the current flows in the opposite direction.

Is that right?

 

[Scottish Chap]

Hey guys,

one more quick question...

I know that in a circuit, electrons travel in the opposite direction than current (I) does. But which direction is it? Do electrons travel from higher voltage to lower voltage (and current travels from lower to higher) or the other way around?

Thanks!!!

Hmmm....I'll assume you're talking about a circuit in the realms of the physics section rather than the slightly more esoteric way the chemists define it for galvanic and electrolytic cells. Charge (defined by physicists as arbitrarily positive) flows from positive to negative and electrons flow in the opposite direction (negative to positive). The current is equally distributed at every point of the circuit. In terms of voltage....that's just what the battery or generator puts out to drive current. If the voltage is 6V going out at the positive end, you know that everything in that circuit (resistors, bulbs etc) must equal a six volt drop in total (and the measured voltage will have the opposite polarity at each ‘drop point’ in the circuit). For example, a circuit with a six volt battery, two resistors, and a bulb may have a -1.5 V drop across each resistor (-3.0V total for resistors) and a -3.0V drop across the bulb (so the whole circuit has a -6V drop). So, the way you phrase it, the electrons will flow from the “lower end potential in this circuit to the higher end potential”. Hope that makes sense!

All the very best on the MCAT tomorrow. I do not envy you. Don’t make the mistake I made by staying up until midnight tonight. I took it last August and thought the PS section was going to be insurmountable--I had never taken a single physics class in my life at that point - even in high school. Still, everything went fine and, in spite of the Draconian MCAT, I'll be an MSI this year.....just like you will be soon.

 

[BaylorGuy]

Current travels from high voltage to low voltage....electrons flow the opposite way. Thus on a battery when you see a positive and a negative, that is the convential current, which flows from positive to negative (but remember that the electrons flow in the opposite direction....neg to pos...WHY?? physicists or chemists screwed it up a long time ago and we are stuck with it now. )

Galvanic--reduction at Cathode (which is positive)...Oxidation at Anode (which is negative). Cell emf is positive, delta G is negative, thus spontaneous (this is the typical battery)

Electrolytic--reduction at Cathode (which is negative in this battery)...Oxidation at Anode (whic is positive). Cell emf is negative, delta G is positive, thus non-spontaneous (this is when recharging the typical battery, if it is rechargeable).

 

[beponychick]

Hmmm....I'll assume you're talking about a circuit in the realms of the physics section rather than the slightly more esoteric way the chemists define it for galvanic and electrolytic cells. Charge (defined by physicists as arbitrarily positive) flows from positive to negative and electrons (current) flow in the opposite direction (negative to positive). The current is equally distributed at every point of the circuit. In terms of voltage....that's just what the battery or generator puts out to drive current. If the voltage is 6V going out at the positive end, you know that everything in that circuit (resistors, bulbs etc) must equal a six volt drop in total (and the measured voltage will have the opposite polarity at each ‘drop point’ in the circuit). For example, a circuit with a six volt battery, two resistors, and a bulb may have a -1.5 V drop across each resistor (-3.0V total for resistors) and a -3.0V drop across the bulb (so the whole circuit has a -6V drop). So, the way you phrase it, the electrons (current) will flow from the “lower end potential in this circuit to the higher end potential”. Hope that makes sense!

All the very best on the MCAT tomorrow. I do not envy you. Don’t make the mistake I made by staying up until midnight tonight. I took it last August and thought the PS section was going to be insurmountable--I had never taken a single physics class in my life at that point - even in high school. Still, everything went fine and, in spite of the Draconian MCAT, I'll be an MSI this year.....just like you will be soon.

Thank you so much. This explanation makes a lot of sense! Thanks for the good wishes too!

 

[beponychick]

Current travels from high voltage to low voltage....electrons flow the opposite way. Thus on a battery when you see a positive and a negative, that is the convential current, which flows from positive to negative (but remember that the electrons flow in the opposite direction....neg to pos...WHY?? physicists or chemists screwed it up a long time ago and we are stuck with it now. )

Galvanic--reduction at Cathode (which is positive)...Oxidation at Anode (which is negative). Cell emf is positive, delta G is negative, thus spontaneous (this is the typical battery)

Electrolytic--reduction at Cathode (which is negative in this battery)...Oxidation at Anode (whic is positive). Cell emf is negative, delta G is positive, thus non-spontaneous (this is when recharging the typical battery, if it is rechargeable).

So cathode is not always -? I memorized the phase "cations go to cathode" which assumes that the cathode is -. But this is not true for a galvanic cell correct?

 

[Wolfkishner]

Hey, someone correct me because I could be wrong...

In a galvanic cell the anode is negative and the cathode is positive, the electrons go towards the positive, thus the current flows in the opposite direction.

In a electrolytic cell the anode is positive and the cathode is negative, the electrons go towards the positive, thus the current flows in the opposite direction.

Is that right? [/QUOTE

Kind of:

For both galvanic and electrolytic cells, electrons enter the cell circuit at the anode and travel to the cathode. Thus electrons move from anode to cathode--remember, no matter what the cell, An Ox Red Cat. Oxidation (loss of e-) occurs at the anode i.e. electrons must be leaving the anode. Reduction (gain of e-) occurs at the cathode i.e. where e- are flowing.

Current is defined as the direction in which a postive charge would flow i.e. the opposite direction of the electron (don't blame me, blame the Physicists ) Thus, for both cells, since electrons are flowing from the anode to the cathode, Current is flowing from the cathode to the anode.

The positive and negative designations on different electrodes are not "charges" they are sign conventions. The anode is negative in a galvanic cell, not because it is negatively "charged," but because it is the source of the circuit electrons i.e. it is generating the flow of electrons. The anode is positive in an electrolytic cell because it is connected to the positive pole of a battery (cathode is connected to the negative pole). In this case, the battery, not the anode, is the source of the electrons. However, remember, they still enter the cell circuit at the anode and flow to the cathode!

So, know that the sign conventions for the half cells (anode/cathode) are different depending on the cell, and know the characteristics (delta G, Emf, etc) of spontaneous/nonspontaneous cells. However, know also that for all cells, electrons always flow/enter the cell circuit at the anode and travel to the cathode, just as current is directed from the cathode to the anode.

Good luck!

 

[Turkeyman]

Reductions always occur at the cathode and oxidations always occur at the anode. Electrons flow from anode to cathode, because the cathode is being reduced. The only diff b/w galvanic and electrolytic cells is their labelling of the cathode/anode as +/- for galvanic cells, and -/+ for electrolytic cells, emf's, and their spontenaity(sorry for sp). Electrolytic cells require a power source which is greater than their negative emf to get them going.

And sorry if I reiterated all the above stellar posts, but I love getting my thoughts together as well

Thanks guys