RI 2025 Electrochemistry (I)

1 RAFFLES INSTITUTION YEAR 6 H2 CHEMISTRY 2025 Lecture Notes 21a – Electrochemistry 1 _______________________________________________________________________________ A Content  Redox processes: electron transfer and changes in oxidation number (oxidation state)  Electrode potentials (i) Standard electrode (redox) potential, E ; the redox series (ii) Standard cell potentials, Ecell, and their uses (iii) Batteries and fuel cells B Learning outcomes Candidates should be able to: (a) describe and explain redox processes in terms of electron transfer and/or of changes in oxidation number (oxidation state) (b) define the terms: (i) standard electrode (redox) potential (ii) standard cell potential (c) describe the standard hydrogen electrode (d) describe methods used to measure the standard electrode potentials of: (i) metals or non–metals in contact with their ions in aqueous solution (ii) ions of the same element in different oxidation states (e) calculate a standard cell potential by combining two standard electrode potentials (f) use standard cell potentials to: (i) explain/deduce the direction of electron flow from a simple cell (ii) predict the spontaneity of a reaction (g) understand the limitations in the use of standard cell potentials to predict the spontaneity of a reaction (h) construct redox equations using the relevant half–equations (i) state and apply the relationship G = – nFE to electrochemical cells, including the calculation of E for combined half reactions (j) predict qualitatively how the value of an electrode potential varies with the concentration of the aqueous ion (k) state the possible advantages of developing other types of cell, e.g. the H 2/O2 fuel cell and improved batteries (as in electric vehicles) in terms of smaller size, lower mass and higher voltage C References 1. Chemistry for Advanced Level by Peter Cann and Peter Hughes 2. Chemistry the Central Science by T L Brown and H E Lemay 3. Chemistry by Zumdahl

2 PRE-REQUISITE KNOWLEDGE Candidates should be able to describe and explain redox processes in terms of electron transfer and/or of changes in oxidation number (oxidation state). Please refer to Lecture Notes 1b Redox Reactions pages 2 – 8 to refresh your understanding on redox reactions and how to balance redox equations. An oxidation number is a number which is assigned to an element in a substance to show its state of oxidation. Note: The oxidation number of an element in a substance is related to the number of electrons lost, gained, or shared as a result of chemical bonding.  A positive change in oxidation state indicates that oxidation (loss of electrons) has occurred e.g. +1, +2.  A negative change in oxidation state indicates that reduction (gain of electrons) has occurred e.g. –1, –2. Rules for