lec5_2011

lec5_2011 - Concentration Cells M | M+(aq, L) | M+(aq, R) |...

This preview shows pages 1–6. Sign up to view the full content.

Concentration Cells M | M + (aq, L) || M + (aq, R) | M Cell reaction: M + (aq, R) → M + (aq, L) E = since Δ r G θ = 0 (why?) E = Q vF RT vF G r ln - - θ R L b b vF RT ln -

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
The cell emf The standard emf of a cell can be calculated by the difference of the standard potentials of the two electrodes. Consider: Ag(s)|Ag + (aq) || Cl - (aq) |AgCl(s)| Ag(s) The overall potential of the cell is: E θ = E θ (AgCl/Ag, Cl - ) – E θ (Ag + /Ag) In a general form: E θ = E θ (right) – E θ (left) Example: Calculate the standard voltage for the cell: Mn +2 |Mn +3 ||Fe +3 |Fe +2 Solution: First, separate the cell into two half reactions Reduction: Fe +3 (aq) + e - → Fe +2 (aq) Reduction: Mn +3 (aq) + e - Mn +2 (s) To compute the cell voltage, simply use the right-hand electrode subtract the left-hand electrode. E θ = E θ right - E θ left = 0.769 - (1.51) = - 0.741 V (???)
Calculating equilibrium constant from the standard emf Example: Evaluate the solubility constant of silver chloride, AgCl, from cell potential data at 298.15K. Solution: AgCl(s) Ag + (aq) + Cl - (aq) Establish the electrode combination: Right: AgCl + e - Ag(s) + Cl - (aq) E θ = 0.22V Left: Ag + (aq) + e - → Ag(s) E θ = 0.80V The standard emf is : E θ (right) – E θ (Left) = - 0.58V ln K = = 0.58/0.025693 K = 1.6x10 -10 RT vFE θ

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
The measurement of standard potentials The potential of standard hydrogen electrode: Pt(s)|H 2 (g)|H + (aq) is defined as 0 at all temperatures. The standard potential of other electrodes can be obtained by constructing an electrochemical cell, in which hydrogen electrode is employed as the left-hand electrode (i.e. anode) Example: the standard potential of the AgCl/Ag couple is the standard emf of the following cell: Pt(s)|H 2 (g)|H + (aq), Cl - (aq)|AgCl(s)|Ag(s) or Pt(s)|H 2 (g)|H + (aq) || Cl - (aq)|AgCl(s)|Ag(s) with the cell reaction is: ½ H 2 (g) + AgCl(s) → H + (aq) + Cl - (aq) + Ag(s)
Δ r G = Δ r G θ + RTln According to Nernst equation:

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 02/14/2011 for the course SCIENCE 321 taught by Professor Aaa during the Spring '11 term at Windsor.

Page1 / 20

lec5_2011 - Concentration Cells M | M+(aq, L) | M+(aq, R) |...

This preview shows document pages 1 - 6. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online