Loss of electrons, increase in oxidation number, gain of oxygen and loss of hydrogen
Gain of electrons, decrease in oxidation number, loss of oxygen and gain of hydrogen
The electrode where oxidation takes place
The electrode where reduction takes place
Define oxidising agent
A species that oxidises another species by removing 1+ electrons, and itself being reduced.
Define reducing agent
A species that reduces another species by adding 1+ electrons, and itself is oxidised
Which direction do electrons flow?
From anode to cathode (oxidation half cell to reduction half cell)
Describe the standard hydrogen electrode
A platinum foil immersed in 1moldm^-3 HCl, enclosed in a tube containing hydrogen gas at standard pressure
What are the standard conditions?
298k, 100kPa (1atm) 1moldm^-3 and elements in their standard states
What is OILRIG?
Oxidation Is Loss (of electrons) Reduction Is Gain (of electrons)
What are the rules for assigning oxidation numbers?
Oxidation number of atoms in elements is always 0
The more electronegative element in the substance has the negative oxidation number and the less electronegative element has the positive oxidation number
Fluorine is always -1
Hydrogen is always +1, except in metal hydrides where it is -1
Oxygen is always -2, except in peroxide where it is -1, and in OF2 it is +2 as fluorine is more electronegative
In neutral molecules the sum of the oxidation numbers is 0
In ions the sum of the oxidation numbers is equal to the charge
What is the standard cell potential?
Voltage measured under standards conditions when a half cell is connected to a standard hydrogen electrode. It tells us how readily a substance releases electrons relative to hydrogen
E(cell) = reduction half cell - oxidation half cell
What is a salt bridge?
Porous substance soaked in a solution of an inert, strong electrolyte. The salt ions flow through the bridge to complete the cell and balance charges in solutions.
Eg. Filter paper soaked in KNO3
What is an electrochemical cell?
Produces electricity from a chemical reaction (combination of 2 half cells)
What is a storage cell?
(Battery) a cell that can be recharged when the current is passed in the opposite way to the current generated by a chemical reaction in the cell.
What is a fuel cell?
A cell used to harness electricity from a chemical reaction (fuel + oxygen). Chemicals are stored separately outside the cell and fed in when electricity is required