Electrochemistry Flashcards
What is Electrochemistry
Is the study of chemical reactions that take place at the surface of an electrode
The reactions that occur at the electrodes are redox reactions in which there is a transfer of electrons between the electrode and the electrolyte , resulting in a change in oxidation state of the elements involved
What is an electrode
Is an electronic conductor (usually a metal) immersed in an electrolyte, which is an ionic conductor (ususally an ionic solution)
What is an electrochemical cell
consists of two electrodes in contact with an electrolyte
(the simplest type of electrochemical cell has a common electrolyte shared between two electrodes)
What is the difference between a Galvanic Cell and an Electrolytic Cell
In a Galvanic cell, electricity is produced when a spontaneous reaction takes place in the cell
In an electrolytic cell a non-spontaneous reaction is driven by an external current
What reaction occurs at the cathode and anode
An oxidation reaction occurs at the anode and electrons released travel through an external circuit to the cathode where a reduction reaction occurs
If a high-resistance voltmeter is connected between electrodes, this measures
the potential difference (or voltage) of cell
Electrochemistry usually involves REDOX reactions, this involves…
Oxidation: loss of electron
Reduction: gain of electrons
Usually electrochemical cells require a different electrolyte for each electrode
What does this look like?
- Two electrodes with their own electrolyte - an anode and cathod
- Connected by a salt bridge which compartmentalises the electrodes and allows the movement of ions
- A voltmeter measures the potential difference
What is a half-reaction
the redox reaction that occurs at the electrode
These half reactions are combined to form the overall cell reaction
What are some general rules for Cell diagrams
- Phase boundaries are denoted by: │
- a salt bride: ││
- the metal electrodes are at the edges
- Electron flow must be from left to right: oxidation on the LHS and reduction on the RHS
Describe a platinum half-cell
The platinum is inert, so is not involved in the electrochemical reaction
The platinum electrode supports the hydrogen gas electrode
And then there is the aqueous solution of H⁺ ions
A half-cell written like this suggests…
Pt(s)│Fe²⁺(aq),Fe³⁺(aq)│
A comma denotes two species in the same phase (for example, both in solution)
A half-cell written like this suggests….
Ag(s)│AgCl(s)│Cl⁻(s)
a metal coated with an insoluble salt of the same metal
A spontaneous cell reaction corresponds with a ……… Gibbs free energy change
Negative
A spontaneous cell reaction corresponds to a ……. cell potential
Positive
The electrical work done by the current flowing in the external circuit is the product of this charge and the potential difference
Hence work is the equation to work out work done AND Gibbs free energy change
What is the chosen standard electrode (and it’s standard states) and why is it used
- The chosen standard is the standard hydrogen electrode which an electrode potential of zero is given. When all species are in their standard states pressure is 1 bar and activity = 1 (usually 298K)
- It is not possible to measure the contribution to the overall cell potential from each individual electrode, so a standard is required, against which relative measurements can be made
The Nernst equation shows how cell potential depends on the concentrations (or activities) of the species involved in the cell reaction
What is the Nernst equation
*Hint it links cell potential and ΔrG
