Electro chemistry
1-Reversibe process
2-Irreversible process
Reversible cells (Galvanic cell )
When the cell says reversible cell?
1- if emf of the cell equal the potential of external power supply (battery)
2- if potential of external power supply › emf of the cell → current pass in the reverse direction , that is mean that the chemical reaction inside the cell pass in the reverse direction.
Cu + Zn+2 → Cu+2 + Zn
3- if the potential of the external battery < emf of the cell → low current pass according to the chemical reaction occur inside the cell.
i.e. Zn + Cu+2 → Zn+2 + Cu
So, the cell which have ( (تتوفر لهاthree conditions called reversible cell.
e.g: Danial cell ((عرض الخلية
Zn /ZnSO4 // CuSO4 / Cu
4-We can restore the constiteunts of cell
1-Reversibe process
2-Irreversible process
Reversible cells (Galvanic cell )
When the cell says reversible cell?
1- if emf of the cell equal the potential of external power supply (battery)
2- if potential of external power supply › emf of the cell → current pass in the reverse direction , that is mean that the chemical reaction inside the cell pass in the reverse direction.
Cu + Zn+2 → Cu+2 + Zn
3- if the potential of the external battery < emf of the cell → low current pass according to the chemical reaction occur inside the cell.
i.e. Zn + Cu+2 → Zn+2 + Cu
So, the cell which have ( (تتوفر لهاthree conditions called reversible cell.
e.g: Danial cell ((عرض الخلية
Zn /ZnSO4 // CuSO4 / Cu
4-We can restore the constiteunts of cell
Rrreversible cells (Rust of Iron)
1- if emf of the cell equal the potential of external power supply (battery)
2- if potential of external power supply › emf of the cell → current pass in the reverse direction , that is mean that the chemical reaction inside the cell pass in the reverse direction.
Cu + Zn+2 → Cu+2 + Zn
3- if the potential of the external battery < emf of the cell → low current pass according to the chemical reaction occur inside the cell.
4-We can not restore the constiteunts of cell
- Galvanic cells
Change the chemical energy to electrical energy through physical or chemical change
The electromotive force “emf” of the galvanic cell produce due to the big difference in potential.
i.e decrease in free energy (∆G=-ve)
i.e Spontaneous process
Types of galvanic cells
1- Chemical cells
Here electrical energy produce due to occur chemical change
a- chemical cells with transfer
b- chemical cells without transfer
2- Concentration cells
Here electrical energy produce due to occur physical change accompany by transfer of mater from place to another
Concentration cells divided into:
i- Electrode concentration cells
a- Gaseous concentration cells
b- Amalgam concentration cells
ii- Electrolytic concentration cells
a- Electrolytic conc. Cells with transfer
b- Electrolytic conc. Cells without transfer
1- if emf of the cell equal the potential of external power supply (battery)
2- if potential of external power supply › emf of the cell → current pass in the reverse direction , that is mean that the chemical reaction inside the cell pass in the reverse direction.
Cu + Zn+2 → Cu+2 + Zn
3- if the potential of the external battery < emf of the cell → low current pass according to the chemical reaction occur inside the cell.
4-We can not restore the constiteunts of cell
- Galvanic cells
Change the chemical energy to electrical energy through physical or chemical change
The electromotive force “emf” of the galvanic cell produce due to the big difference in potential.
i.e decrease in free energy (∆G=-ve)
i.e Spontaneous process
Types of galvanic cells
1- Chemical cells
Here electrical energy produce due to occur chemical change
a- chemical cells with transfer
b- chemical cells without transfer
2- Concentration cells
Here electrical energy produce due to occur physical change accompany by transfer of mater from place to another
Concentration cells divided into:
i- Electrode concentration cells
a- Gaseous concentration cells
b- Amalgam concentration cells
ii- Electrolytic concentration cells
a- Electrolytic conc. Cells with transfer
b- Electrolytic conc. Cells without transfer
[ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذه الصورة]
What is the electrode reactions?
The reactions that occur due to the transfer of electrons to or from the electrode
In galvanic cells, the oxidation process occur at the anode and take – ve sign
While the reduction process occur at the cathode and take + ve sign
This is the reverse of electrolytic cell
The electrode can write by its name M/Mc+n
Notes:
If emf +ve sign means spon. Process, ∆G= -ve
If emf -ve sign means non-spon. Process, ∆G = +ve
Since, emf = L + R
Measurements of E0, for pure metals- P 1 atm- activity of solution =1
– express the potential of electrodes by reduction potential (ما لم ينص غي غير ذلك)
e.g: E0 = - 0.76 v for Zn
That is mean that E0 (Zn+2/Zn) = - 0.76 v
Applications of electrochemistry:
1- Electrochemical batteries
2- Fuel cells
3- Metal finishing
4- Refining and production of metal
5- Metals and material processing
6- Corrosion control
7- Electrolysis
8- Determination of physical parameters.
E.g. K, equilibrium constant, E0 stander cell potential, PH , reaction rates and …..
9- Titration (coductomertric, potentiometric)
10- Recycling of industrial
What is the electrode reactions?
The reactions that occur due to the transfer of electrons to or from the electrode
In galvanic cells, the oxidation process occur at the anode and take – ve sign
While the reduction process occur at the cathode and take + ve sign
This is the reverse of electrolytic cell
The electrode can write by its name M/Mc+n
Notes:
If emf +ve sign means spon. Process, ∆G= -ve
If emf -ve sign means non-spon. Process, ∆G = +ve
Since, emf = L + R
Measurements of E0, for pure metals- P 1 atm- activity of solution =1
– express the potential of electrodes by reduction potential (ما لم ينص غي غير ذلك)
e.g: E0 = - 0.76 v for Zn
That is mean that E0 (Zn+2/Zn) = - 0.76 v
Applications of electrochemistry:
1- Electrochemical batteries
2- Fuel cells
3- Metal finishing
4- Refining and production of metal
5- Metals and material processing
6- Corrosion control
7- Electrolysis
8- Determination of physical parameters.
E.g. K, equilibrium constant, E0 stander cell potential, PH , reaction rates and …..
9- Titration (coductomertric, potentiometric)
10- Recycling of industrial
Before we speak about the postulates of the theory, first we must know the factors affecting on the electrode potential:
1- The metal solution pressure (SP)
2- Osmotic pressure of solution (OP), i.e concentration of solution around the electrode.
Osmosis: It is the flow of solvent molecules from pure solvent to the solution through semi permeable membrane separate between them.
Osmotic pressure π: It is the pressure required to be applied on the solution to prevent the flow of solvent molecules to the solution.
3- Temperatures
4- Valence of metal ions.
لو القضيب سالب بالتالي تحيط به الالكترونات
i.e ability of the metal to loss electrons >ability of metal ion to deposit
i.e Ox process is occur
Here, potential difference i.e. there
i.e ability of metal ion to gain electrons then change to metal deposit >ability of metal to dissolve
i.e red process occur
·˙· metal become +ve charged Here, potential difference i.e. there are electrode potential
هذا في حالة القضيب الموجب
In this case no charge is formed i.e no edl is formed
·˙· no potential difference,
i.e. there is no electrode potential
وهذا في حاله القضيب او القطب المتعادل بدون اي شحنات
منقول مع بعض التعديلات بما يوافق المحاضره