electrochemistry involves two main types of processes
DESCRIPTION
ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES. A. Voltaic(galvanic) cells – which are spontaneous chemical reactions (battery) B. Electrolytic cells – which are non-spontaneous and require external e− source (DC power source) - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/1.jpg)
Electrochemistry
ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES
• A. Voltaic(galvanic) cells – which are spontaneous chemical reactions (battery)
• B. Electrolytic cells – which are non-spontaneous and require external e− source (DC power source)
• C. BOTH of these fit into the category entitled Electrochemical cells
![Page 2: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/2.jpg)
Electrochemistry
Oxidation Numbers
In order to keep track of what loses electrons and what gains them, we assign oxidation numbers.
![Page 3: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/3.jpg)
Electrochemistry
Oxidation and Reduction
• A species is oxidized when it loses electrons.Here, zinc loses two electrons to go from neutral
zinc metal to the Zn2+ ion.
![Page 4: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/4.jpg)
Electrochemistry
Oxidation and Reduction
• A species is reduced when it gains electrons.Here, each of the H+ gains an electron and they
combine to form H2.
![Page 5: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/5.jpg)
Electrochemistry
Oxidation and Reduction
• What is reduced is the oxidizing agent.H+ oxidizes Zn by taking electrons from it.
• What is oxidized is the reducing agent.Zn reduces H+ by giving it electrons.
![Page 6: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/6.jpg)
Electrochemistry
Assigning Oxidation Numbers
1. Elements in their elemental form have an oxidation number of 0.
2. The oxidation number of a monatomic ion is the same as its charge.
![Page 7: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/7.jpg)
Electrochemistry
Voltaic Cells
In spontaneous oxidation-reduction (redox) reactions, electrons are transferred and energy is released.
![Page 8: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/8.jpg)
Electrochemistry
Voltaic Cells
• We can use that energy to do work if we make the electrons flow through an external device.
• We call such a setup a voltaic cell.
![Page 9: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/9.jpg)
Electrochemistry
Voltaic Cells
• A typical cell looks like this.
• The oxidation occurs at the anode.
• The reduction occurs at the cathode.
![Page 10: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/10.jpg)
Electrochemistry
Voltaic Cells
The flow of electrons is always from the anode to the cathode through the wire
![Page 11: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/11.jpg)
Electrochemistry
Voltaic Cells
Once even one electron flows from the anode to the cathode, the charges in each beaker would not be balanced and the flow of electrons would stop.
![Page 12: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/12.jpg)
Electrochemistry
Voltaic Cells
• Therefore, we use a salt bridge, usually a U-shaped tube that contains a salt solution, to keep the charges balanced.Cations move toward
the cathode.Anions move toward
the anode.
![Page 13: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/13.jpg)
Electrochemistry
Voltaic Cells• In the cell, then,
electrons leave the anode and flow through the wire to the cathode.
• As the electrons leave the anode, the cations formed dissolve into the solution in the anode compartment.
![Page 14: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/14.jpg)
Electrochemistry
Voltaic Cells• As the electrons
reach the cathode, cations in the cathode are attracted to the now negative cathode.
• The electrons are taken by the cation, and the neutral metal is deposited on the cathode.
![Page 15: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/15.jpg)
Electrochemistry
Voltaic Cells Animation
![Page 16: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/16.jpg)
Electrochemistry
Electromotive Force (emf)• Water only
spontaneously flows one way in a
waterfall.• Likewise, electrons
only spontaneously flow one way in a
redox reaction—from higher to lower
potential energy.
![Page 17: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/17.jpg)
Electrochemistry
Cell Potential (Electromotive Force (emf))
• The potential difference between the anode and cathode in a cell is called the electromotive force (emf).
• It is also called the cell potential, and is designated Ecell.
![Page 18: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/18.jpg)
Electrochemistry
Cell Potential (Electromotive Force (emf))
• Each potential is measured against a standard , which is the standard hydrogen electrode [consists of a piece
• of inert Platinum that is bathed by hydrogen gas at 1 atm]. The hydrogen electrode is assigned a value
• of ZERO volts.
![Page 19: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/19.jpg)
Electrochemistry
Cell Potential (Electromotive Force (emf))
• standard conditions—1 atm for gases, 1.0M for solutions and 25°C for all (298 K)
• • naught (°)--we use the naught to symbolize standard conditions [Experiencing a thermo flashback?] • That means• Ecell, Emf, or εcell become • Ecello , Emfo , or εcello when measurements are taken
at standard conditions. You’ll soon learn how these change when the conditions are nonstandard!
![Page 20: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/20.jpg)
Electrochemistry
Reduction Potential Chart
• elements that have the most positive reduction potentials are easily reduced (in general, non-metals)
• elements that have the least positive reduction potentials are easily oxidized (in general, metals)
• The table can also be used to tell the strength of various oxidizing and reducing agents.
• Can also be used as an activity series. Metals having less positive reduction potentials are more active
and will replace metals with more positive potentials.
![Page 21: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/21.jpg)
Electrochemistry
Standard Reduction Potentials
Reduction potentials for
many electrodes have been
measured and tabulated.
![Page 22: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/22.jpg)
Electrochemistry
Writing a Cell Diagram-Standard Cell notation“ion sandwich in alphabetical order”
• The reduced species is written on the right hand side—this electrode is the cathode
• The oxidized species is placed on the left hand side and this is the anode.
• For example the cell diagram of a zinc and copper galvanic cell:
• A vertical line (I ) represents the different phases present in each half cell-phase boundary. (if in same phase use comma instead)
• A double vertical line II represents the salt bridge connecting the two half cells
• Anode I solution II cathode solution I cathode
![Page 23: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/23.jpg)
Electrochemistry
Zn(s) I Zn +2 II Cu+2 I Cu (s)• Zinc and Lead(s) (plumbous) • • Copper and iron+3 and +2 (use copper
II)
![Page 24: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/24.jpg)
Electrochemistry
What do you do when one of your electrodes lacks a SOLID METAL??
You will need an inert conductor (usually platinum ) put in parentheses (Pt)
Different species of the same phase are separated by a comma• Fe+3 (aq) + Cu(s) Cu+2 + Fe2+
![Page 25: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/25.jpg)
Electrochemistry
Calculating Standard Cell Potential (Ecello , Emfo , or εcello )
• Decide which element is oxidized or reduced using the standard reduction potential chart. Element with more positive reduction potential gets reduced!
• Write both equations as is from the chart with their voltage• Reverse the equation that will be oxidized and change the sign
of the voltage• Balance the two half reactions BUT DO NOT MULTIPLY
VOLTAGE VALUES• Add the two half reactions and their voltages together • Ecello = Eo
oxidation + Eoreduction where o
means standard conditions 1atm , 1M and 25oC
![Page 26: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/26.jpg)
Electrochemistry
Calculate Cell Potential E cello
• Zinc and lead (s) Plumbous
• Copper and iron+3 and +2 (use copper II)
1. H2 (g) + I2 (g) 2H+ (aq) + 2 I – (aq)
![Page 27: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/27.jpg)
Electrochemistry
Calculate Cell Potential E celloDraw a diagram of the galvanic cell for the reaction and
label completely
• Fe+3 (aq) + Cu(s) Cu+2 + Fe2+
![Page 28: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/28.jpg)
Electrochemistry
Cell Potential , Electrical Work, And Free energy
Cell potential is measured in volts (V).It is the work that can be accomplished when electrons are transferred through a wire.
1 V = 1 Work(J) Charge ( C)
![Page 29: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/29.jpg)
Electrochemistry
Cell Potential , Electrical Work, And Free energy
1 joule of work is required or produced when one coloumb of charge is transferred between two points
1 V = 1 Work(J) Charge ( C)
![Page 30: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/30.jpg)
Electrochemistry
Cell Potential , Electrical Work, And Free energy
• Using the table of standard reduction potentials, calculate G o for the reaction:
• Cu+2(aq) + Fe(S) Cu (s) + Fe+2 (aq)
• • IS it spontaneous?
![Page 31: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/31.jpg)
Electrochemistry
Cell Potential , Electrical Work, And Free energyG o = - nFEo
• G= Gibb’s Free energy• n= numbers of moles of electrons • F= Faraday constant 96500 J/V . Mol• The redox reaction will be spontaneous
when G o = _________• The redox reaction will be spontaneous
when Eo = __________•
![Page 32: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/32.jpg)
Electrochemistry
Cell Potential , Electrical Work, And Free energyG o = - nFEo
+
G o = - RT ln K =• You can derive the equation: for Ecell
at standard conditions at equilibrium
Eo = RT ln K nF
![Page 33: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/33.jpg)
Electrochemistry
Eo = RT ln K nF
K Eo G o ConclusionGreater than 1
Positive negative
=1 0 0Less than one
Negative positive
![Page 34: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/34.jpg)
Electrochemistry
•Nernst Equation
E = E − RTnF ln Q
•Why?It is used to calculate the voltage generated by the combination of two half-cells when the conditions are not standard!!!!!!!• n= numbers of electrons transferred between species• F= Faraday constant 96500 J/V . mol • R=ideal gas constant 8.314 /K mol• T= Kelvin Temperature• Eo= the voltage generated if the conditions
» were standard• Q= reactions quotient [products]x
• [reactants]y
![Page 35: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/35.jpg)
Electrochemistry
If the reaction below is carried out using solutions that are 5.0 M Zn +2 and 0.3 M Cu+2 at 298 K, what is the actual cell voltage? Zn (s) + Cu+2
Cu(s) + Zn+2
• Step 1: Work out Eo cell assuming standard conditions:
• • • Step 2: Calculate Q (don’t forget _____ and _______
are omitted from Q)• • • • Step 3: Find n• • Step 4: Plug everything in! (Answer 1.06 V)
![Page 36: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/36.jpg)
Electrochemistry
Assigning Oxidation Numbers
3. Nonmetals tend to have negative oxidation numbers, although some are positive in certain compounds or ions.
Oxygen has an oxidation number of −2, except in the peroxide ion in which it has an oxidation number of −1.
Hydrogen is −1 when bonded to a metal, +1 when bonded to a nonmetal.
![Page 37: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/37.jpg)
Electrochemistry
Assigning Oxidation Numbers
3. Nonmetals tend to have negative oxidation numbers, although some are positive in certain compounds or ions.
Fluorine always has an oxidation number of −1.
The other halogens have an oxidation number of −1 when they are negative; they can have positive oxidation numbers, however, most notably in oxyanions.
![Page 38: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/38.jpg)
Electrochemistry
Assigning Oxidation Numbers
4. The sum of the oxidation numbers in a neutral compound is 0.
5. The sum of the oxidation numbers in a polyatomic ion is the charge on the ion.
![Page 39: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/39.jpg)
Electrochemistry
Balancing Oxidation-Reduction Equations
Perhaps the easiest way to balance the equation of an oxidation-reduction reaction is via the half-reaction method.
![Page 40: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/40.jpg)
Electrochemistry
Balancing Oxidation-Reduction Equations
This involves treating (on paper only) the oxidation and reduction as two separate processes, balancing these half reactions, and then combining them to attain the balanced equation for the overall reaction.
![Page 41: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/41.jpg)
Electrochemistry
Half-Reaction Method
1. Assign oxidation numbers to determine what is oxidized and what is reduced.
2. Write the oxidation and reduction half-reactions.
![Page 42: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/42.jpg)
Electrochemistry
Half-Reaction Method
3. Balance each half-reaction.a. Balance elements other than H and O.b. Balance O by adding H2O.c. Balance H by adding H+.d. Balance charge by adding electrons.
4. Multiply the half-reactions by integers so that the electrons gained and lost are the same.
![Page 43: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/43.jpg)
Electrochemistry
Half-Reaction Method
5. Add the half-reactions, subtracting things that appear on both sides.
6. Make sure the equation is balanced according to mass.
7. Make sure the equation is balanced according to charge.
![Page 44: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/44.jpg)
Electrochemistry
Half-Reaction Method
Consider the reaction between MnO4− and C2O4
2− :
MnO4−(aq) + C2O4
2−(aq) Mn2+(aq) + CO2(aq)
![Page 45: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/45.jpg)
Electrochemistry
Half-Reaction Method
First, we assign oxidation numbers.
MnO4− + C2O4
2- Mn2+ + CO2
+7 +3 +4+2
Since the manganese goes from +7 to +2, it is reduced.
Since the carbon goes from +3 to +4, it is oxidized.
![Page 46: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/46.jpg)
Electrochemistry
Oxidation Half-Reaction
C2O42− CO2
To balance the carbon, we add a coefficient of 2:
C2O42− 2 CO2
![Page 47: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/47.jpg)
Electrochemistry
Oxidation Half-Reaction
C2O42− 2 CO2
The oxygen is now balanced as well. To balance the charge, we must add 2 electrons to the right side.
C2O42− 2 CO2 + 2 e−
![Page 48: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/48.jpg)
Electrochemistry
Reduction Half-Reaction
MnO4− Mn2+
The manganese is balanced; to balance the oxygen, we must add 4 waters to the right side.
MnO4− Mn2+ + 4 H2O
![Page 49: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/49.jpg)
Electrochemistry
Reduction Half-Reaction
MnO4− Mn2+ + 4 H2O
To balance the hydrogen, we add 8 H+ to the left side.
8 H+ + MnO4− Mn2+ + 4 H2O
![Page 50: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/50.jpg)
Electrochemistry
Reduction Half-Reaction
8 H+ + MnO4− Mn2+ + 4 H2O
To balance the charge, we add 5 e− to the left side.
5 e− + 8 H+ + MnO4− Mn2+ + 4 H2O
![Page 51: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/51.jpg)
Electrochemistry
Combining the Half-Reactions
Now we evaluate the two half-reactions together:
C2O42− 2 CO2 + 2 e−
5 e− + 8 H+ + MnO4− Mn2+ + 4 H2O
To attain the same number of electrons on each side, we will multiply the first reaction by 5 and the second by 2.
![Page 52: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/52.jpg)
Electrochemistry
Combining the Half-Reactions
5 C2O42− 10 CO2 + 10 e−
10 e− + 16 H+ + 2 MnO4− 2 Mn2+ + 8 H2O
When we add these together, we get:
10 e− + 16 H+ + 2 MnO4− + 5 C2O4
2−
2 Mn2+ + 8 H2O + 10 CO2 +10 e−
![Page 53: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/53.jpg)
Electrochemistry
Combining the Half-Reactions
10 e− + 16 H+ + 2 MnO4− + 5 C2O4
2− 2 Mn2+ + 8 H2O + 10 CO2 +10 e−
The only thing that appears on both sides are the electrons. Subtracting them, we are left with:
16 H+ + 2 MnO4− + 5 C2O4
2− 2 Mn2+ + 8 H2O + 10 CO2
![Page 54: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/54.jpg)
Electrochemistry
Balancing in Basic Solution
• If a reaction occurs in basic solution, one can balance it as if it occurred in acid.
• Once the equation is balanced, add OH− to each side to “neutralize” the H+ in the equation and create water in its place.
• If this produces water on both sides, you might have to subtract water from each side.
![Page 55: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/55.jpg)
Electrochemistry
Standard Hydrogen Electrode
• Their values are referenced to a standard hydrogen electrode (SHE).
• By definition, the reduction potential for hydrogen is 0 V:
2 H+ (aq, 1M) + 2 e− H2 (g, 1 atm)
![Page 56: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/56.jpg)
Electrochemistry
Standard Cell Potentials
The cell potential at standard conditions can be found through this equation:
Ecell = Ered (cathode) − Ered (anode)
Because cell potential is based on the potential energy per unit of charge, it is an intensive property.
![Page 57: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/57.jpg)
Electrochemistry
Cell Potentials• For the oxidation in this cell,
• For the reduction,
Ered = −0.76 V
Ered = +0.34 V
![Page 58: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/58.jpg)
Electrochemistry
Cell Potentials
Ecell = Ered (cathode) − Ered (anode)
= +0.34 V − (−0.76 V)= +1.10 V
![Page 59: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/59.jpg)
Electrochemistry
Oxidizing and Reducing Agents
• The strongest oxidizers have the most positive reduction potentials.
• The strongest reducers have the most negative reduction potentials.
![Page 60: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/60.jpg)
Electrochemistry
Oxidizing and Reducing Agents
The greater the difference between the two, the greater the voltage of the cell.
![Page 61: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/61.jpg)
Electrochemistry
Nernst Equation
• Remember thatG = G + RT ln Q
• This means−nFE = −nFE + RT ln Q
![Page 62: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/62.jpg)
Electrochemistry
Nernst Equation
Dividing both sides by −nF, we get the Nernst equation:
E = E − RTnF ln Q
or, using base-10 logarithms,
E = E − 2.303 RTnF ln Q
![Page 63: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/63.jpg)
Electrochemistry
Concentration Cells
• Notice that the Nernst equation implies that a cell could be created that has the same substance at both electrodes.
• For such a cell, would be 0, but Q would not.Ecell
• Therefore, as long as the concentrations are different, E will not be 0.
![Page 64: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/64.jpg)
Electrochemistry
Applications of Oxidation-Reduction
Reactions
![Page 65: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/65.jpg)
Electrochemistry
Batteries
![Page 66: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/66.jpg)
Electrochemistry
Alkaline Batteries
![Page 67: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/67.jpg)
Electrochemistry
Hydrogen Fuel Cells
![Page 68: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/68.jpg)
Electrochemistry
Corrosion and…
![Page 69: ELECTROCHEMISTRY INVOLVES TWO MAIN TYPES OF PROCESSES](https://reader036.vdocuments.mx/reader036/viewer/2022081420/56815dff550346895dcc41db/html5/thumbnails/69.jpg)
Electrochemistry
…Corrosion Prevention