Chapter 20 - Electrode Potentials and Electrochemical Cells Flashcards
What is an electrochemical cell?
It is a cell where a redox reaction takes place but the electrons are transferred indirectly via an external circuit. This causes a potential difference between the two cells which drives an electric current to do work
What are uses of electrochemical cells?
They can be used for portable batteries (which have lots of uses). In larger scales, they can be used to power cars
What is the form of most half-equations for electrode reactions?
M + e- -> <- M- (reaction could instead involve positive ions and the transfer of electrons involved with them, particularly in the case of metals)
What is the convential representation of an entire cell?
It is usually a beaker with a liquid and an electrode which is connected via an external cicuit to another beaker and its electrode. The two beakers however are also connected via a salt bridge
What is the reference for all electrode potentials?
All electrode potentials are measured relative to a half electrode of hydrogen, with an Edelta 0 value, and everything is either greater or lesser than the hydrogen half cell depending on the work done by the cell and the movement of electrons
How do stronger reducing agents behave when added to a solution of a salt of their ions?
Stronger reducing agents more easily give their electrons up, whereas strong oxidising agents struggle to give them up but instead are stronger at accepting the electrons
Why are standardised conditions so important when comparing the reducing power (how negative an emf value) different metals have?
Because concentration of metal ions and temperature can have a large impact on the Edelta value, therefore standard conditions are needed to fairly and accurately assess the reducing power
What are the standard conditions of a standard electrode potential, Edelta (or emf (electromotive force))
298K
100 kPa (if a gas is being used)
1 mol per dm3 of solution
If an element is being testing which is not conductive (e.g hydrogen), what is used instead of an electrode of the metal?
A platinum electrode, and the gas is bubbled into the beaker
What is the salt bridge used for?
1) it completes the circuit and allows electrons to move
2) it uses its own ions to balance any electronic charge induced in the cell to allow electrons to keep moving
What is the most typical and simple electrode cell used in portable electronics? Give the reactions at the positive and negative electrode
Lithium electrodes:
positive : Li+ + CoO2 + e- -> Li[CoO2]-
negative: Li -> Li+ + e- (the electrode here is made of carbon)
Give the reactions present in a hydrogen - oxygen fuel cell
2H2 + 4OH- -> 4H2O + 4e-
O2 + 2H2O + 4e- -> 4OH-
What is a fuel cell?
A fuel cell are where the two different “fuels” or electrolytes are seperated by a semi-permeable membrane
