Electrochemistry Flashcards
What does more positive E mean
More spontaneous/more favoured
Standard cell potential equation
And R constant
Slide 2
Reduction happens where
Gain of electrons
Cathode
Red cat
Oxidation happens where
Loss of electrons
Anode
An ox
Q= I x t
Q is what
I
t
Charge in coloumbs
Current in Amps (C/second)
Time (in seconds)
What is current
The flow of electrons
Connection of current to moles of electrons moved
Slide 3
Explain how we can control a reductions reaction based on controlling the potential of the electrode
If my electrode has one electron and wants to transfer it to solution A
It would transfer it to the LUMO of A which is higher in energy the the electrode right now, This is unfavourable
We put more energy into the electrode (give it more negative potential and more electrons) and make it higher than the LUMO in energy
now the electron can transfer to LUMO favourably and go down in energy after the transfer
Explain how we can control a oxidation reaction based on controlling the potential of the electrode
We want an electron from A to move to the orbital of the anode
But the anode is higher in energy than A
So we add more postive potential to the electrode to make it lower in energy
Then A can transfer an electron to the lower energy electrode
What is fermi
The highest natural energy of the electrode
Explain how a current graph works
At the level where the line is straight on the x axis, not redox reaction happen
As the current and voltage (potential) goes (positive) the energy level of electrode goes down, and oxidation reaction happen
As current goes negative, the energy level of the electrode goes up and reduction happens
If a reduction is happing what type of potential is it
Cathodic potential
What is over potential
Thermodynamics potential
The extra voltage always needed to overcome the activation energy of the electron transfer (to let the reaction fully Likely happen)
The Nernst E is the thermodynamic potential which is the minimum energy need to make the reaction favourable
Why do we need overpotential
To overcome the activation energy of a in solution reaction
To overcome the activation energy of a counter reaction (there always reduction and oxidation, two reactions, so there no charge buildup)
To nucleate bubbles when gas forms (smooth need higher overpotential vs rough electrodes)
To overcome electrical resistance of the solution (V=IR)
What are the counter reactions that happen
Oxygen reduction or h2 oxidation
Also a voltage (V=IR) drop due to voltage being lost over a distance
What is an electrical double layer
This it at the surface of the electrode where the electrodes negatively charged surface attracts postive charges in the solution
This caused a double layer of - + charge
The other ions spread out through the rest of the solution
What is E when far from the electrode
0
What is the three electrode cell
Usually there’s the ref electrode and the working electrode
We don’t touch the ref electrode
A counter electrode is added to avoid passing current through the RE and changing its concentrations/potential
This counter electrode has high surface area and is inert to prevent unwanted reactions on the ref electrode
What is electrolysis
Using a potentiostat to drive a less favourable reaction forward
to usually deposit a solid product
What is a potentio stat
A thing used to control and measure both potential and current
What happens during an electrolysis
The concentration of the analyte goes down which makes the E go down too
(Nernst potential needed to reduce analyte is more negative (1/[]))
This change makes interferents in the solution start to react, and water starts to break down
What do we do to counter the effects of electrolysis
We need to change the E (potential) at the CATHODE
adjusts for the drop in cu concentration and keeps the overall E constant
If potential goes too negative what happens
Too postive
Too negative, H2 is made
Too +, O2 is made
All by breaking down water
Slide 11 equations
Put in sheet
What is electrogravimetric analysis
What does the graph tell is
Depositing all of the metal from the solution into a mesh with large surface area at the cathode when reduced
The start of the graph is the overpotential then the reduction occurs as potential gets more negative
More -V means more -I (current), as v gets more negative the reduction of h20 to h2 happens (two reaction begin to happens)
In a mix of na cl and h20 how do you know what I’ll reduce and be oxidized
By the potentials in the equations redox equations.
Cl2 reduction has postive E so it won’t reduce
IDK LOOK UP
What is coloumetry
What is kept constant
Measuring the coloumbs (charge transferred) in a reaction to see for far the reaction goes
Also called chronocoulometry since current and time are being measured
Only one of either the current or potential is held constant, and the other changes
In coloumetry, what gives the total charge (I) in relation to mols of the thing that reacted
The area under the curve of the graph
In coloumetry, why does the current drop off over time (decrease)
The reactant concentration decreases over time and the reaction goes more slowly
A small amount of capacitave current is needed to rearrange the ions in the double layer
