Finding Half Reactions

1
Finding Half Reactions

• Keep in mind that not all electrochemical
  reactions will be a simple two-reactant, two
  product system.
• From a cell drawing or line diagram, you should
  look for elements in two oxidation states to
  write the half reactions e.g.

2
Equilibrium Constants and Electrochemistry

• The spontaneous reaction from a galvanic cell
  occurs because the system is not at equilibrium
• E for the net reaction can thus be related to K

3
Equilibrium Constant Example

• Find the equilibrium constant
• This can be divided into two half reactions

4
Cells as Probes

• There are two types of equilibria associated with
  a galvanic cell
• Equilibrium between two half-cells
• Equilibrium within each half-cell

In the right cell, the following reaction can
take place The Ksp reaction in the half-cell is
in equilibrium
The cell can be thought of as an analytical probe
for H, since it is the only species we do not
have a concentration for.
5
Tough Problems

• You can have some tough problems (the book calls
  them brainbusters) involving electrochemistry,
  equilibrium, solubility, and acid-base chemistry.
• I havent assigned those, but in case you were to
  face this, you should know generally how to
  tackle them
• 1) Write half-reactions and potentials
• 2)Write Nernst equation for the net reaction and
  put in all the knowns.
• 3) Solve for that unknown and plug it into the
  equilibrium equation for the problem

6
Redox Reactions in Biochemistry

• Many redox reactions are important in
  biochemistry, especially in respiration
• Biochemists use a the term of formal potential,
  meant to define potentials under conditions of
  biochemistry
• Formal potential is given the abbreviation Eº

7
Important Biochemical Reactions