1. Electrochemistry Lesson 2
Galvanic cell
Cell notation
Predict spontaneous redox rxn
Sketch a galvanic cell & calculate Ecell

2. Galvanic Cell also Galvanic (Voltaic) Electrochemical Cells
Uses redox reactions
Transform chemical potential energy into electrical energy

3. Components of a galvanic cell
Electrolyte
conducts an electric current when dissolved in water
electrolytes are in separated cells; no direct contact
Electrode
2 different metals
Anode: the electrode at which OXIDATION occurs  i.e. the (-) end
- a negative electrode where e- originate from
Cathode: the electrode at which REDUCTION occurs  i.e. the (+) end
A wire connects the 2 electrodes to allow movement of electrons from the ANODE to the cathode
A voltmeter or ammeter can be connected to the wire to measure voltage or current
Salt bridge
A U-shaped glass tube, filled with an ionic salt (aq), that connects the two half cells & close the circuit
Allows a current to flow but prevents contact between oxidizing agent (OA) and reducing agent (RA)

4. Cell notation= short hand notation of a galvanic cell
because if the oxidizing agent and reducing agent in a galvanic cell were not separated, the chemical energy of the transferred electrons would be released into the environment as thermal energy and could not be harnessed to do useful work.
Write the equation
Occurring at each electrode:
Cell notation:

5. Mnemonic Devices 

6. Deduce a general rule of how to write a cell notation
Or Zn(s) | Zn2+(aq) || Cu2+(aq) | Cu(s)
phase boundary
phase boundary
Salt bridge
e- flow from anode to cathode

7. How to predict if a redox rxn is spontaneous or not?
Use the table of relative strengths of oxidizing and reducing agents (will call it the E cell table)
- if the oxidizing agent (OA) is ABOVE the reducing agent (RA), rxn is spontaneous
See attached table

8. Zn(s) + Cu2+(aq)  Zn2+(aq) + Cu(s) (spontaneous)
Strongest OA ↓
Weakest OA
Cu2+(aq) + 2e-  Cu(s)
Weakest RA ↑
Strongest RA
Zn2+(aq) + 2e-  Zn(s)
Zn(s) Cu2+(aq)  Zn2+(aq) + Cu(s) (spontaneous)
Stronger OA
But if you react:
Zn2+(aq) + Cu(s)  Zn(s) + Cu2+(aq) (non-spontaneous)
Weaker OA

9. Redox Spontaneity prediction practice
Which of the following metals is the strongest RA? Cr, Mg, Fe, Co, Ni
2. Describe each reaction as spontaneous or non-spontaneous
Au+3 + Fe+2 → Fe Au
Pb + Fe+3 → Fe Pb+2
Magnesium
a) NS b) S
3. Which of the following pairs of ions cannot exist simultaneously in aqueous solutions (i.e. will spontaneously react)? If the reaction is spontaneous, write a balanced equation for the reaction that would occur
a. Cu2+ and Fe b. Au3+ and Fe

10. Redox Spontaneity answers
Which of the following metals is the strongest RA?
Cr, Mg, Fe, Co, Ni
2. Describe each reaction as spontaneous or non-spontaneous
Au+3 + Fe+3 → Fe Au (Non-spon)
Pb + Fe+3 → Fe Pb+2 (spon.)
Magnesium
a) NS b) S

11. Cell potential (Voltage)
A measure of the potential energy from an electrochemical cell
E cell table lists the Reduction Potential for each half reaction
This value is determined by comparing each half reaction to a reference cell (Hydrogen half-cell) which is designated as zero
2H+(aq) e- ⇋ H2(g) Eor = 0.00V at SATP

12. Calculate the standard cell potential for any electrochemical cell
Eocell = Eoreduction + Eooxidation
For the oxidation half-reaction, Eooxidation = - Eoreduction.
If E°cell > 0, rxn is spontaneous
If E°cell < 0, rxn is non-spontaneous
All galvanic cells are spontaneous (E°cell > 0)

13. Sketch the galvanic cell for following overall reaction.
Show :  direction of e- flow direction of ion migration
identify the cathode & anode
Give the overall balanced reaction  calculate the ∆E° Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s)
Step 1 - Write the equation and standard potential for each reduction reaction
Zn2+(aq) + 2 e-  Zn(s Eoreduction of Zn2+ = V
Cu2+(aq) + 2 e-   Cu(s) Eoreduction of Cu2+ = V

14. B/c Eocell > 0, rxn is spontaneous
Step 2 – Determining the cathode and anode
The half-rxn with a more positive value gets to be the reduction reaction  keep the rxn as is
The half-rxn with a less positive value is the oxidation reaction  flip the reaction and reverse the sign of E°
Add the cell potentials together to get the overall standard cell potential.
B/c Eocell > 0, rxn is spontaneous

15. Sketch the cell Cell Notation Zn(s) | Zn2+(aq) || Cu2+(aq) | Cu(s)
Figure from p636 txtbook
Cell Notation Zn(s) | Zn2+(aq) || Cu2+(aq) | Cu(s)
 e- flow from the Zn anode to the Cu cathode
The Zn electrode decreases in mass, the Cu electrode increase in mass
Cl- ions move from the salt bridge to Zn half-cell to counterbalance the gain in positive charge of Zn2+
Na+ ions move from the salt bridge to the Cu half-cell to counterbalance the loss of Cu2+ positive charge

16. Design an electrochemical cell to electroplate a metal object with copper
Materials given:
Copper pennies
10-cent pennies or a metal key
Vinegar
Conductors
Battery