Redox + Electrode Potentials Flashcards
reduction
Gain of electrons or decrease in oxidation number
Oxidation
Loss of electrons or increase in oxidation number
oxidising agent
(Contains species that’s being reduced)
A reagent that oxidises (takes electrons from) another species
Oxidising agent GAINS ELECTRONS
Reducing agent
(Contains species that’s being oxidised)
A reagent that reduces (gives electrons to) another species
A reducing agent LOSES ELECTRONS
What is oxidation number of an uncombined element
0
What is oxidation number of combined H
+1
What is oxidation number of combined O
-2
What is oxidation number of an ion of an element equal to
It’s ionic charge
E.g. Ca^2+ = +2
What is oxidation number of H in metal hydrides
-1
E.g. NaH , CaH2
What is oxidation number of O in peroxides
-1
E.g. H2O2
What is oxidation number of O bonded to F
+2
E.g. F2O
Entropy
The quantitative measure of the degree of disorder in a system (S)
UNITS JK^-1mol^-1
The entropy change can be calculated by
sum of product entropies- sum of reactant entropies
What are standard conditions
Temperature of 298K, pressure of 100kPa and all solutions have concentrations of 1moldm^3
When a metal is in contact with a solution of its ions…
An equilibrium is established where electrons accumulate on surface and the metal develops a NEGATIVE CHARGE
the more reactive a metal, the more likely it is to _____ electrons
The more reactive a metal the more likely it is to LOSE electrons
What is a half cell
A metal in contact with an aqueous solution of its ions
What is an electrochemical cell (aka voltaic cell)
when 2 half cells are connected together
- high resistance voltmeter
- salt bridge of KNO3
Why must 2 half cells be kept apart?
If allowed to mix, electrons would flow in an uncontrolled way and heat energy would be released rather than electrical energy
metal/ metal ion half cells
Metal rod dipped in solution of its aqueous metal ions
E.g. Zn2+(aq) / Zn(s)
ion/ion half cells
Contains ions of the same element in different oxidation states (there’s no solid) A INERT PLATINUM ELECTRODE MUST BE USED
E.g. Fe2+(aq),Fe3+(aq)/ Pt(s)
the electrode with the more reactive metal _____ electrons and is ______ this is the ______ electrode
The electrode with the more reactive metal LOSES ELECTRONS and is OXIDISED this is the NEGATIVE electrode
the electrode with the less reactive metal _____ electrons and is ______ this is the ______ electrode
The electrode with the less reactive metal GAINS ELECTRONS and is REDUCED this is the POSITIVE ELECTRODE
standard electrode potential
of a half cell is the emf of the half cell where a standard hydrogen electrode is used as the reference electrode and is carried out under standard conditions (298K, 100kPa, 1moldm^-3)
