Battery
An electrochemical cell that converts chemical energy into electrical energy through redox reactions.
What do highly reactive metals (group I and II metals, excluding Be) tend to form when reacting with water?
metal hydroxides
What do less reactive metals form when reacting with steam?
metal oxides
Electrochemical cells
Systems in which redox reactions happen.
Whey are electrochemical cells called electrochemical cells?
Because there is a transfer of electrons due to chemical reactions in cells.
What are the 2 types of electrochemical cells?
Voltaic cells (primary cells) and electrolytic cells
Voltaic cell
An electrochemical cell that converts energy from spontaneous exothermic chemical reactions to electrical energy (converts chemical energy to electrical energy).
Energy is released and electricity is produced.
Electrolytic cell
An electrochemical cell that converts electrical energy to chemical energy by bringing about non-spontaneous reactions.
Energy (a power source) is required.
Electrodes
Conductors of electricity used to make contact with the electrolyte.
Two electrodes, an anode and a cathode, are required in an electrochemical cell.
Anode
The electrode where oxidation takes place.
Cathode
The electrode where reduction takes place.
State and explain the polarity in voltaic cells
Anodes are negative, cathodes are positive.
Electrons are released at the anode as oxidation takes place at the anode and the species undergoing oxidation releases electrons, hence a negative polarity at the anode and a positive polarity at the cathode.
State and explain the polarity in electrolytic cells
Anodes are positive, cathodes are negative.
Electrons are released at the cathode by the battery, hence a negative polarity at the cathode and a positive polarity at the anode.
Polarity of the two electrodes
The polarity refers to the relative charge of the two electrodes in the cell.
Where electrons are being released, there is more negative charge, making it the negative pole.
Electrolyte
The non-metallic part of a circuit
What value (positive or negative) should the voltmeter give as energy/electricity is being produced in a voltaic cell?
Positive
State the role of the salt bridge, and explain how the salt bridge works.
The salt bridge will allow the continuous flow of electrons on the external wire, as it provides a liquid junction between the two half-cells with free-to-move ions, reducing the liquid-junction potential as ions can move in and out of the salt-bridge.
As electrons flow from the anode to the cathode through the external wire, there will be a build up of negative charge at the cathode. Cations from the salt bridge will move to the cathode. In the anode, there will be a build up of positive charge, and so anions will move to the anode, reducing the liquid-junction potential.
Liquid-junction potential (not part of the syllabus, but explains the role of the salt bridge)
A voltage generated at the interface of two electrolyte solutions with different compositions or concentrations, caused by unequal diffusion rates of ions.
Suitable salt bridge ions should be…
Inert.
Phase boundary (|)
Junction, the surface of the metal in contact with the solution/electrolyte.
Are voltaic cells rechargeable? Why or why not?
Voltaic cells are not rechargeable because the chemical reactions that produce electricity are irreversible.
Rechargeable batteries
Batteries that use reversible redox/chemical reactions to provide energy to power sources.
They are reusable.
How are rechargeable batteries recharged?
The chemical reaction is reversed by the use of an electrical current to drive the reaction back to its original state, functioning as an electrolytic cell.
Standard electrode potential
The electrode potential of a half-reaction under SATP conditions relative to the standard hydrogen potential.
Used to quantify whether one element will more readily undergo oxidation or reduction compared to another element.
