chem aqa a level help!!

hello guys i was confused on something in electrochemical cells

In my notes it says that reduction occurs at the positive electrode and oxidation occurs at the negative electrode however at gcse we learnt in electrolysis that its the other way round? please can someone explain this to me :/

Reply 1

Nitrotoluene

Original post

by Frizzle16523

hello guys i was confused on something in electrochemical cells
In my notes it says that reduction occurs at the positive electrode and oxidation occurs at the negative electrode however at gcse we learnt in electrolysis that its the other way round? please can someone explain this to me :/

Hey there! I understand that's a confusing concept when you're learning about electrochemical cells. The key point to focus on is the kind of cell in use here:
Galvanic Cells (or Voltaic Cells): These cells generate electrical energy from spontaneous chemical reactions, such as batteries.
Electrolytic Cells:
-Use electrical energy to drive non-spontaneous chemical reactions
-Similar to galvanic cells, but in reverse: instead of generating electricity, electrolytic cells use electricity to facilitate chemical reactions that wouldn't occur naturally
Now, let’s unpack why the electrode signs and which end oxidation and reduction occurs are different:
Galvanic Cells (Generating Electricity):
Here's the gist:
- Anode (Negative Electrode): This is where oxidation happens, and it lets out electrons.
- Cathode (Positive Electrode): This is where reduction takes place, and it takes in electrons.
So, the anode is negative because it releases electrons, while the cathode is positive because it accepts them. Just remember, the anode isn’t loaded with electrons; it's negative since it's giving them off, and the cathode is positive because it’s where the electrons go.
Cathode (Positive Electrode):
This is where the reduction happens. Positive ions take in electrons and turn into metallic atoms or other reduced forms.
Galvanic Cells Reminder:
Think of "AN OX RED CAT" to remember that oxidation happens at the anode and reduction at the cathode.
As for electron flow:
- The anode (negative end) gives off electrons.
- The cathode (positive end) takes in them.
Electrolytic Cells (Using Electricity):
Step (Positive Electrode):
-Oxidation occurs, but driven by an external electric current
-Positive ions gain electrons to form neutral metal
-This process makes the step positively charged, as the external power source draws electrons away

Cathode (Negative Electrode):
-Reduction occurs, driven by an external power source supplying electrons
-Positive ions receive electrons and become neutral
-As a result, the cathode becomes negative

Mnemonic:

-AN OX and RED CAT still apply, but since the power source controls electron flow, the signs reverse:
-Anode (positive) releases electrons
-Cathode (negative) accepts electrons
Bye,
Sandro

Reply 2

Frizzle16523

Original post

by Nitrotoluene

Hey there! I understand that's a confusing concept when you're learning about electrochemical cells. The key point to focus on is the kind of cell in use here:
Galvanic Cells (or Voltaic Cells): These cells generate electrical energy from spontaneous chemical reactions, such as batteries.
Electrolytic Cells:
-Use electrical energy to drive non-spontaneous chemical reactions
-Similar to galvanic cells, but in reverse: instead of generating electricity, electrolytic cells use electricity to facilitate chemical reactions that wouldn't occur naturally
Now, let’s unpack why the electrode signs and which end oxidation and reduction occurs are different:
Galvanic Cells (Generating Electricity):
Here's the gist:
- Anode (Negative Electrode): This is where oxidation happens, and it lets out electrons.
- Cathode (Positive Electrode): This is where reduction takes place, and it takes in electrons.
So, the anode is negative because it releases electrons, while the cathode is positive because it accepts them. Just remember, the anode isn’t loaded with electrons; it's negative since it's giving them off, and the cathode is positive because it’s where the electrons go.
Cathode (Positive Electrode):
This is where the reduction happens. Positive ions take in electrons and turn into metallic atoms or other reduced forms.
Galvanic Cells Reminder:
Think of "AN OX RED CAT" to remember that oxidation happens at the anode and reduction at the cathode.
As for electron flow:
- The anode (negative end) gives off electrons.
- The cathode (positive end) takes in them.
Electrolytic Cells (Using Electricity):
Step (Positive Electrode):
-Oxidation occurs, but driven by an external electric current
-Positive ions gain electrons to form neutral metal
-This process makes the step positively charged, as the external power source draws electrons away
Cathode (Negative Electrode):
-Reduction occurs, driven by an external power source supplying electrons
-Positive ions receive electrons and become neutral
-As a result, the cathode becomes negative

Mnemonic:

-AN OX and RED CAT still apply, but since the power source controls electron flow, the signs reverse:
-Anode (positive) releases electrons
-Cathode (negative) accepts electrons
Bye,
Sandro

so basically its the other way round as the type of cells in electrochemical cells and electrolysis are different?

Reply 3

Nitrotoluene

Original post

by Frizzle16523

so basically its the other way round as the type of cells in electrochemical cells and electrolysis are different?

That's a great question! A critical distinction between electrochemical cells and electrolysis that you rightly note.
The two types of cells work almost in inverse ways. But they’re not entirely different beasts. Here’s a quick rundown:
Electrochemical cells (or voltaic/galvanic cells):
These devices generate electrical energy from spontaneous chemical reactions.
For example, consider batteries. The chemical reactions that take place inside occur spontaneously and create electricity.
In these types of cells, the anode is negative, where oxidation occurs, and the cathode is positive, where reduction occurs.
Electrolytic Cells:
– These cells consume electrical energy to drive chemical reactions that would not occur spontaneously.
– This process is known as electrolysis. To function, you must apply power (from a battery, for example).
Others include electroplating, creating aluminum, and splitting water into hydrogen and oxygen.
– In this case, the anode must be the positive end, so it’s connected to the positive side of the power source, and the cathode is the negative end connected to the negative side.
So, the main differences are:
Cell reactions: Spontaneous for the galvanic/voltaic cell; nonspontaneous in the electrolytic cell.
The direction of energy transfer is chemical to electrical energy transfer in electrochemical cells and electrical to chemical energy transfer in electrolytic cells.
Power source: Not required for galvanic cells, and required for electrolytic cells
Electrode polarity: The anode and cathode reverse between the two cell types.

Bye,
Sandro

(edited 11 months ago)

Reply 4

natylamine

hey!
honestly the confusion is totally understandable however first thing my teacher told us before starting this topic is to completely forget that electrolysis exists because it is compleeeeteeely different, goodluck !

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